Readability.js

/*
 * Copyright (c) 2010 Arc90 Inc
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * This code is heavily based on Arc90's readability.js (1.7.1) script
 * available at: http://code.google.com/p/arc90labs-readability
 */

/**
 * Public constructor.
 * @param {HTMLDocument} doc     The document to parse.
 * @param {Object}       options The options object.
 */
function Readability(doc, options) {
  // In some older versions, people passed a URI as the first argument. Cope:
  if (options && options.documentElement) {
    doc = options;
    options = arguments[2];
  } else if (!doc || !doc.documentElement) {
    throw new Error(
      "First argument to Readability constructor should be a document object.",
    );
  }
  options = options || {};

  this._doc = doc;
  this._docJSDOMParser = this._doc.firstChild.__JSDOMParser__;
  this._articleTitle = null;
  this._articleByline = null;
  this._articleDir = null;
  this._articleSiteName = null;
  this._attempts = [];

  // Configurable options
  this._debug = !!options.debug;
  this._maxElemsToParse = options.maxElemsToParse ||
    this.DEFAULT_MAX_ELEMS_TO_PARSE;
  this._nbTopCandidates = options.nbTopCandidates ||
    this.DEFAULT_N_TOP_CANDIDATES;
  this._charThreshold = options.charThreshold || this.DEFAULT_CHAR_THRESHOLD;
  this._classesToPreserve = this.CLASSES_TO_PRESERVE.concat(
    options.classesToPreserve || [],
  );
  this._keepClasses = !!options.keepClasses;
  this._serializer = options.serializer || function (el) {
    return el.innerHTML;
  };
  this._disableJSONLD = !!options.disableJSONLD;
  this._allowedVideoRegex = options.allowedVideoRegex || this.REGEXPS.videos;

  // Start with all flags set
  this._flags = this.FLAG_STRIP_UNLIKELYS |
    this.FLAG_WEIGHT_CLASSES |
    this.FLAG_CLEAN_CONDITIONALLY;

  // Control whether log messages are sent to the console
  if (this._debug) {
    const logNode = function (node) {
      if (node.nodeType == node.TEXT_NODE) {
        return `${node.nodeName} ("${node.textContent}")`;
      }
      const attrPairs = Array.from(node.attributes || [], function (attr) {
        return `${attr.name}="${attr.value}"`;
      }).join(" ");
      return `<${node.localName} ${attrPairs}>`;
    };
    this.log = function () {
      if (typeof console !== "undefined") {
        const args = Array.from(arguments, (arg) => {
          if (arg && arg.nodeType == this.ELEMENT_NODE) {
            return logNode(arg);
          }
          return arg;
        });
        args.unshift("Reader: (Readability)");
        console.log.apply(console, args);
      } else if (typeof dump !== "undefined") {
        /* Window dump */
        const msg = Array.prototype.map.call(arguments, function (x) {
          return (x && x.nodeName) ? logNode(x) : x;
        }).join(" ");
        dump("Reader: (Readability) " + msg + "\n");
      }
    };
  } else {
    this.log = function () {};
  }
}

Readability.prototype = {
  FLAG_STRIP_UNLIKELYS: 0x1,
  FLAG_WEIGHT_CLASSES: 0x2,
  FLAG_CLEAN_CONDITIONALLY: 0x4,

  // https://developer.mozilla.org/en-US/docs/Web/API/Node/nodeType
  ELEMENT_NODE: 1,
  TEXT_NODE: 3,

  // Max number of nodes supported by this parser. Default: 0 (no limit)
  DEFAULT_MAX_ELEMS_TO_PARSE: 0,

  // The number of top candidates to consider when analysing how
  // tight the competition is among candidates.
  DEFAULT_N_TOP_CANDIDATES: 5,

  // Element tags to score by default.
  DEFAULT_TAGS_TO_SCORE: "section,h2,h3,h4,h5,h6,p,td,pre".toUpperCase().split(
    ",",
  ),

  // The default number of chars an article must have in order to return a result
  DEFAULT_CHAR_THRESHOLD: 500,

  // All of the regular expressions in use within readability.
  // Defined up here so we don't instantiate them repeatedly in loops.
  REGEXPS: {
    // NOTE: These two regular expressions are duplicated in
    // Readability-readerable.js. Please keep both copies in sync.
    unlikelyCandidates:
      /-ad-|ai2html|banner|breadcrumbs|combx|comment|community|cover-wrap|disqus|extra|footer|gdpr|header|legends|menu|related|remark|replies|rss|shoutbox|sidebar|skyscraper|social|sponsor|supplemental|ad-break|agegate|pagination|pager|popup|yom-remote/i,
    okMaybeItsACandidate: /and|article|body|column|content|main|shadow/i,

    positive:
      /article|body|content|entry|hentry|h-entry|main|page|pagination|post|text|blog|story/i,
    negative:
      /-ad-|hidden|^hid$| hid$| hid |^hid |banner|combx|comment|com-|contact|foot|footer|footnote|gdpr|masthead|media|meta|outbrain|promo|related|scroll|share|shoutbox|sidebar|skyscraper|sponsor|shopping|tags|tool|widget/i,
    extraneous:
      /print|archive|comment|discuss|e[\-]?mail|share|reply|all|login|sign|single|utility/i,
    byline: /byline|author|dateline|writtenby|p-author/i,
    replaceFonts: /<(\/?)font[^>]*>/gi,
    normalize: /\s{2,}/g,
    videos:
      /\/\/(www\.)?((dailymotion|youtube|youtube-nocookie|player\.vimeo|v\.qq)\.com|(archive|upload\.wikimedia)\.org|player\.twitch\.tv)/i,
    shareElements: /(\b|_)(share|sharedaddy)(\b|_)/i,
    nextLink: /(next|weiter|continue|>([^\|]|$)|»([^\|]|$))/i,
    prevLink: /(prev|earl|old|new|<|«)/i,
    tokenize: /\W+/g,
    whitespace: /^\s*$/,
    hasContent: /\S$/,
    hashUrl: /^#.+/,
    srcsetUrl: /(\S+)(\s+[\d.]+[xw])?(\s*(?:,|$))/g,
    b64DataUrl: /^data:\s*([^\s;,]+)\s*;\s*base64\s*,/i,
    // Commas as used in Latin, Sindhi, Chinese and constious other scripts.
    // see: https://en.wikipedia.org/wiki/Comma#Comma_constiants
    commas: /\u002C|\u060C|\uFE50|\uFE10|\uFE11|\u2E41|\u2E34|\u2E32|\uFF0C/g,
    // See: https://schema.org/Article
    jsonLdArticleTypes:
      /^Article|AdvertiserContentArticle|NewsArticle|AnalysisNewsArticle|AskPublicNewsArticle|BackgroundNewsArticle|OpinionNewsArticle|ReportageNewsArticle|ReviewNewsArticle|Report|SatiricalArticle|ScholarlyArticle|MedicalScholarlyArticle|SocialMediaPosting|BlogPosting|LiveBlogPosting|DiscussionForumPosting|TechArticle|APIReference$/,
  },

  UNLIKELY_ROLES: [
    "menu",
    "menubar",
    "complementary",
    "navigation",
    "alert",
    "alertdialog",
    "dialog",
  ],

  DIV_TO_P_ELEMS: new Set([
    "BLOCKQUOTE",
    "DL",
    "DIV",
    "IMG",
    "OL",
    "P",
    "PRE",
    "TABLE",
    "UL",
  ]),

  ALTER_TO_DIV_EXCEPTIONS: ["DIV", "ARTICLE", "SECTION", "P"],

  PRESENTATIONAL_ATTRIBUTES: [
    "align",
    "background",
    "bgcolor",
    "border",
    "cellpadding",
    "cellspacing",
    "frame",
    "hspace",
    "rules",
    "style",
    "valign",
    "vspace",
  ],

  DEPRECATED_SIZE_ATTRIBUTE_ELEMS: ["TABLE", "TH", "TD", "HR", "PRE"],

  // The commented out elements qualify as phrasing content but tend to be
  // removed by readability when put into paragraphs, so we ignore them here.
  PHRASING_ELEMS: [
    // "CANVAS", "IFRAME", "SVG", "VIDEO",
    "ABBR",
    "AUDIO",
    "B",
    "BDO",
    "BR",
    "BUTTON",
    "CITE",
    "CODE",
    "DATA",
    "DATALIST",
    "DFN",
    "EM",
    "EMBED",
    "I",
    "IMG",
    "INPUT",
    "KBD",
    "LABEL",
    "MARK",
    "MATH",
    "METER",
    "NOSCRIPT",
    "OBJECT",
    "OUTPUT",
    "PROGRESS",
    "Q",
    "RUBY",
    "SAMP",
    "SCRIPT",
    "SELECT",
    "SMALL",
    "SPAN",
    "STRONG",
    "SUB",
    "SUP",
    "TEXTAREA",
    "TIME",
    "const",
    "WBR",
  ],

  // These are the classes that readability sets itself.
  CLASSES_TO_PRESERVE: ["page"],

  // These are the list of HTML entities that need to be escaped.
  HTML_ESCAPE_MAP: {
    "lt": "<",
    "gt": ">",
    "amp": "&",
    "quot": '"',
    "apos": "'",
  },

  /**
   * Run any post-process modifications to article content as necessary.
   *
   * @param Element
   * @return void
   */
  _postProcessContent: function (articleContent) {
    // Readability cannot open relative uris so we convert them to absolute uris.
    this._fixRelativeUris(articleContent);

    this._simplifyNestedElements(articleContent);

    if (!this._keepClasses) {
      // Remove classes.
      this._cleanClasses(articleContent);
    }
  },

  /**
   * Iterates over a NodeList, calls `filterFn` for each node and removes node
   * if function returned `true`.
   *
   * If function is not passed, removes all the nodes in node list.
   *
   * @param NodeList nodeList The nodes to operate on
   * @param Function filterFn the function to use as a filter
   * @return void
   */
  _removeNodes: function (nodeList, filterFn) {
    // Avoid ever operating on live node lists.
    if (this._docJSDOMParser && nodeList._isLiveNodeList) {
      throw new Error("Do not pass live node lists to _removeNodes");
    }
    for (let i = nodeList.length - 1; i >= 0; i--) {
      const node = nodeList[i];
      const parentNode = node.parentNode;
      if (parentNode) {
        if (!filterFn || filterFn.call(this, node, i, nodeList)) {
          parentNode.removeChild(node);
        }
      }
    }
  },

  /**
   * Iterates over a NodeList, and calls _setNodeTag for each node.
   *
   * @param NodeList nodeList The nodes to operate on
   * @param String newTagName the new tag name to use
   * @return void
   */
  _replaceNodeTags: function (nodeList, newTagName) {
    // Avoid ever operating on live node lists.
    if (this._docJSDOMParser && nodeList._isLiveNodeList) {
      throw new Error("Do not pass live node lists to _replaceNodeTags");
    }
    for (const node of nodeList) {
      this._setNodeTag(node, newTagName);
    }
  },

  /**
   * Iterate over a NodeList, which doesn't natively fully implement the Array
   * interface.
   *
   * For convenience, the current object context is applied to the provided
   * iterate function.
   *
   * @param  NodeList nodeList The NodeList.
   * @param  Function fn       The iterate function.
   * @return void
   */
  _forEachNode: function (nodeList, fn) {
    Array.prototype.forEach.call(nodeList, fn, this);
  },

  /**
   * Iterate over a NodeList, and return the first node that passes
   * the supplied test function
   *
   * For convenience, the current object context is applied to the provided
   * test function.
   *
   * @param  NodeList nodeList The NodeList.
   * @param  Function fn       The test function.
   * @return void
   */
  _findNode: function (nodeList, fn) {
    return Array.prototype.find.call(nodeList, fn, this);
  },

  /**
   * Iterate over a NodeList, return true if any of the provided iterate
   * function calls returns true, false otherwise.
   *
   * For convenience, the current object context is applied to the
   * provided iterate function.
   *
   * @param  NodeList nodeList The NodeList.
   * @param  Function fn       The iterate function.
   * @return Boolean
   */
  _someNode: function (nodeList, fn) {
    return Array.prototype.some.call(nodeList, fn, this);
  },

  /**
   * Iterate over a NodeList, return true if all of the provided iterate
   * function calls return true, false otherwise.
   *
   * For convenience, the current object context is applied to the
   * provided iterate function.
   *
   * @param  NodeList nodeList The NodeList.
   * @param  Function fn       The iterate function.
   * @return Boolean
   */
  _everyNode: function (nodeList, fn) {
    return Array.prototype.every.call(nodeList, fn, this);
  },

  /**
   * Concat all nodelists passed as arguments.
   *
   * @return ...NodeList
   * @return Array
   */
  _concatNodeLists: function () {
    const slice = Array.prototype.slice;
    const args = slice.call(arguments);
    const nodeLists = args.map(function (list) {
      return slice.call(list);
    });
    return Array.prototype.concat.apply([], nodeLists);
  },

  _getAllNodesWithTag: function (node, tagNames) {
    if (node.querySelectorAll) {
      return node.querySelectorAll(tagNames.join(","));
    }
    return [].concat.apply(
      [],
      tagNames.map(function (tag) {
        const collection = node.getElementsByTagName(tag);
        return Array.isArray(collection) ? collection : Array.from(collection);
      }),
    );
  },

  /**
   * Removes the class="" attribute from every element in the given
   * subtree, except those that match CLASSES_TO_PRESERVE and
   * the classesToPreserve array from the options object.
   *
   * @param Element
   * @return void
   */
  _cleanClasses: function (node) {
    const classesToPreserve = this._classesToPreserve;
    const className = (node.getAttribute("class") || "")
      .split(/\s+/)
      .filter(function (cls) {
        return classesToPreserve.indexOf(cls) != -1;
      })
      .join(" ");

    if (className) {
      node.setAttribute("class", className);
    } else {
      node.removeAttribute("class");
    }

    for (node = node.firstElementChild; node; node = node.nextElementSibling) {
      this._cleanClasses(node);
    }
  },

  /**
   * Converts each <a> and <img> uri in the given element to an absolute URI,
   * ignoring #ref URIs.
   *
   * @param Element
   * @return void
   */
  _fixRelativeUris: function (articleContent) {
    const baseURI = this._doc.baseURI;
    const documentURI = this._doc.documentURI;
    function toAbsoluteURI(uri) {
      // Leave hash links alone if the base URI matches the document URI:
      if (baseURI == documentURI && uri.charAt(0) == "#") {
        return uri;
      }

      // Otherwise, resolve against base URI:
      try {
        return new URL(uri, baseURI).href;
      } catch (_ex) {
        // Something went wrong, just return the original:
      }
      return uri;
    }

    const links = this._getAllNodesWithTag(articleContent, ["a"]);
    this._forEachNode(links, function (link) {
      const href = link.getAttribute("href");
      if (href) {
        // Remove links with javascript: URIs, since
        // they won't work after scripts have been removed from the page.
        if (href.indexOf("javascript:") === 0) {
          // if the link only contains simple text content, it can be converted to a text node
          if (
            link.childNodes.length === 1 &&
            link.childNodes[0].nodeType === this.TEXT_NODE
          ) {
            const text = this._doc.createTextNode(link.textContent);
            link.parentNode.replaceChild(text, link);
          } else {
            // if the link has multiple children, they should all be preserved
            const container = this._doc.createElement("span");
            while (link.firstChild) {
              container.appendChild(link.firstChild);
            }
            link.parentNode.replaceChild(container, link);
          }
        } else {
          link.setAttribute("href", toAbsoluteURI(href));
        }
      }
    });

    const medias = this._getAllNodesWithTag(articleContent, [
      "img",
      "picture",
      "figure",
      "video",
      "audio",
      "source",
    ]);

    this._forEachNode(medias, function (media) {
      const src = media.getAttribute("src");
      const poster = media.getAttribute("poster");
      const srcset = media.getAttribute("srcset");

      if (src) {
        media.setAttribute("src", toAbsoluteURI(src));
      }

      if (poster) {
        media.setAttribute("poster", toAbsoluteURI(poster));
      }

      if (srcset) {
        const newSrcset = srcset.replace(
          this.REGEXPS.srcsetUrl,
          function (_, p1, p2, p3) {
            return toAbsoluteURI(p1) + (p2 || "") + p3;
          },
        );

        media.setAttribute("srcset", newSrcset);
      }
    });
  },

  _simplifyNestedElements: function (articleContent) {
    let node = articleContent;

    while (node) {
      if (
        node.parentNode && ["DIV", "SECTION"].includes(node.tagName) &&
        !(node.id && node.id.startsWith("readability"))
      ) {
        if (this._isElementWithoutContent(node)) {
          node = this._removeAndGetNext(node);
          continue;
        } else if (
          this._hasSingleTagInsideElement(node, "DIV") ||
          this._hasSingleTagInsideElement(node, "SECTION")
        ) {
          const child = node.children[0];
          for (let i = 0; i < node.attributes.length; i++) {
            child.setAttribute(
              node.attributes[i].name,
              node.attributes[i].value,
            );
          }
          node.parentNode.replaceChild(child, node);
          node = child;
          continue;
        }
      }

      node = this._getNextNode(node);
    }
  },

  /**
   * Get the article title as an H1.
   *
   * @return string
   */
  _getArticleTitle: function () {
    const doc = this._doc;
    let curTitle = "";
    let origTitle = "";

    try {
      curTitle = origTitle = doc.title.trim();

      // If they had an element with id "title" in their HTML
      if (typeof curTitle !== "string") {
        curTitle = origTitle = this._getInnerText(
          doc.getElementsByTagName("title")[0],
        );
      }
    } catch (_e) { /* ignore exceptions setting the title. */ }

    let titleHadHierarchicalSeparators = false;
    function wordCount(str) {
      return str.split(/\s+/).length;
    }

    // If there's a separator in the title, first remove the final part
    if ((/ [\|\-\\\/>»] /).test(curTitle)) {
      titleHadHierarchicalSeparators = / [\\\/>»] /.test(curTitle);
      curTitle = origTitle.replace(/(.*)[\|\-\\\/>»] .*/gi, "$1");

      // If the resulting title is too short (3 words or fewer), remove
      // the first part instead:
      if (wordCount(curTitle) < 3) {
        curTitle = origTitle.replace(/[^\|\-\\\/>»]*[\|\-\\\/>»](.*)/gi, "$1");
      }
    } else if (curTitle.indexOf(": ") !== -1) {
      // Check if we have an heading containing this exact string, so we
      // could assume it's the full title.
      const headings = this._concatNodeLists(
        doc.getElementsByTagName("h1"),
        doc.getElementsByTagName("h2"),
      );
      const trimmedTitle = curTitle.trim();
      const match = this._someNode(headings, function (heading) {
        return heading.textContent.trim() === trimmedTitle;
      });

      // If we don't, let's extract the title out of the original title string.
      if (!match) {
        curTitle = origTitle.substring(origTitle.lastIndexOf(":") + 1);

        // If the title is now too short, try the first colon instead:
        if (wordCount(curTitle) < 3) {
          curTitle = origTitle.substring(origTitle.indexOf(":") + 1);
          // But if we have too many words before the colon there's something weird
          // with the titles and the H tags so let's just use the original title instead
        } else if (wordCount(origTitle.substr(0, origTitle.indexOf(":"))) > 5) {
          curTitle = origTitle;
        }
      }
    } else if (curTitle.length > 150 || curTitle.length < 15) {
      const hOnes = doc.getElementsByTagName("h1");

      if (hOnes.length === 1) {
        curTitle = this._getInnerText(hOnes[0]);
      }
    }

    curTitle = curTitle.trim().replace(this.REGEXPS.normalize, " ");
    // If we now have 4 words or fewer as our title, and either no
    // 'hierarchical' separators (\, /, > or ») were found in the original
    // title or we decreased the number of words by more than 1 word, use
    // the original title.
    const curTitleWordCount = wordCount(curTitle);
    if (
      curTitleWordCount <= 4 &&
      (!titleHadHierarchicalSeparators ||
        curTitleWordCount !=
          wordCount(origTitle.replace(/[\|\-\\\/>»]+/g, "")) - 1)
    ) {
      curTitle = origTitle;
    }

    return curTitle;
  },

  /**
   * Prepare the HTML document for readability to scrape it.
   * This includes things like stripping javascript, CSS, and handling terrible markup.
   *
   * @return void
   */
  _prepDocument: function () {
    const doc = this._doc;

    // Remove all style tags in head
    this._removeNodes(this._getAllNodesWithTag(doc, ["style"]));

    if (doc.body) {
      this._replaceBrs(doc.body);
    }

    this._replaceNodeTags(this._getAllNodesWithTag(doc, ["font"]), "SPAN");
  },

  /**
   * Finds the next node, starting from the given node, and ignoring
   * whitespace in between. If the given node is an element, the same node is
   * returned.
   */
  _nextNode: function (node) {
    let next = node;
    while (
      next &&
      (next.nodeType != this.ELEMENT_NODE) &&
      this.REGEXPS.whitespace.test(next.textContent)
    ) {
      next = next.nextSibling;
    }
    return next;
  },

  /**
   * Replaces 2 or more successive <br> elements with a single <p>.
   * Whitespace between <br> elements are ignored. For example:
   *   <div>foo<br>bar<br> <br><br>abc</div>
   * will become:
   *   <div>foo<br>bar<p>abc</p></div>
   */
  _replaceBrs: function (elem) {
    this._forEachNode(this._getAllNodesWithTag(elem, ["br"]), function (br) {
      let next = br.nextSibling;

      // Whether 2 or more <br> elements have been found and replaced with a
      // <p> block.
      let replaced = false;

      // If we find a <br> chain, remove the <br>s until we hit another node
      // or non-whitespace. This leaves behind the first <br> in the chain
      // (which will be replaced with a <p> later).
      while ((next = this._nextNode(next)) && (next.tagName == "BR")) {
        replaced = true;
        const brSibling = next.nextSibling;
        next.parentNode.removeChild(next);
        next = brSibling;
      }

      // If we removed a <br> chain, replace the remaining <br> with a <p>. Add
      // all sibling nodes as children of the <p> until we hit another <br>
      // chain.
      if (replaced) {
        const p = this._doc.createElement("p");
        br.parentNode.replaceChild(p, br);

        next = p.nextSibling;
        while (next) {
          // If we've hit another <br><br>, we're done adding children to this <p>.
          if (next.tagName == "BR") {
            const nextElem = this._nextNode(next.nextSibling);
            if (nextElem && nextElem.tagName == "BR") {
              break;
            }
          }

          if (!this._isPhrasingContent(next)) {
            break;
          }

          // Otherwise, make this node a child of the new <p>.
          const sibling = next.nextSibling;
          p.appendChild(next);
          next = sibling;
        }

        while (p.lastChild && this._isWhitespace(p.lastChild)) {
          p.removeChild(p.lastChild);
        }

        if (p.parentNode.tagName === "P") {
          this._setNodeTag(p.parentNode, "DIV");
        }
      }
    });
  },

  _setNodeTag: function (node, tag) {
    this.log("_setNodeTag", node, tag);
    if (this._docJSDOMParser) {
      node.localName = tag.toLowerCase();
      node.tagName = tag.toUpperCase();
      return node;
    }

    const replacement = node.ownerDocument.createElement(tag);
    while (node.firstChild) {
      replacement.appendChild(node.firstChild);
    }
    node.parentNode.replaceChild(replacement, node);
    if (node.readability) {
      replacement.readability = node.readability;
    }

    for (let i = 0; i < node.attributes.length; i++) {
      try {
        replacement.setAttribute(
          node.attributes[i].name,
          node.attributes[i].value,
        );
      } catch (_ex) {
        /* it's possible for setAttribute() to throw if the attribute name
         * isn't a valid XML Name. Such attributes can however be parsed from
         * source in HTML docs, see https://github.com/whatwg/html/issues/4275,
         * so we can hit them here and then throw. We don't care about such
         * attributes so we ignore them.
         */
      }
    }
    return replacement;
  },

  /**
   * Prepare the article node for display. Clean out any inline styles,
   * iframes, forms, strip extraneous <p> tags, etc.
   *
   * @param Element
   * @return void
   */
  _prepArticle: function (articleContent) {
    this._cleanStyles(articleContent);

    // Check for data tables before we continue, to avoid removing items in
    // those tables, which will often be isolated even though they're
    // visually linked to other content-ful elements (text, images, etc.).
    this._markDataTables(articleContent);

    this._fixLazyImages(articleContent);

    // Clean out junk from the article content
    this._cleanConditionally(articleContent, "form");
    this._cleanConditionally(articleContent, "fieldset");
    this._clean(articleContent, "object");
    this._clean(articleContent, "embed");
    this._clean(articleContent, "footer");
    this._clean(articleContent, "link");
    this._clean(articleContent, "aside");

    // Clean out elements with little content that have "share" in their id/class combinations from final top candidates,
    // which means we don't remove the top candidates even they have "share".

    const shareElementThreshold = this.DEFAULT_CHAR_THRESHOLD;

    this._forEachNode(articleContent.children, function (topCandidate) {
      this._cleanMatchedNodes(topCandidate, function (node, matchString) {
        return this.REGEXPS.shareElements.test(matchString) &&
          node.textContent.length < shareElementThreshold;
      });
    });

    this._clean(articleContent, "iframe");
    this._clean(articleContent, "input");
    this._clean(articleContent, "textarea");
    this._clean(articleContent, "select");
    this._clean(articleContent, "button");
    this._cleanHeaders(articleContent);

    // Do these last as the previous stuff may have removed junk
    // that will affect these
    this._cleanConditionally(articleContent, "table");
    this._cleanConditionally(articleContent, "ul");
    this._cleanConditionally(articleContent, "div");

    // replace H1 with H2 as H1 should be only title that is displayed separately
    this._replaceNodeTags(
      this._getAllNodesWithTag(articleContent, ["h1"]),
      "h2",
    );

    // Remove extra paragraphs
    this._removeNodes(
      this._getAllNodesWithTag(articleContent, ["p"]),
      function (paragraph) {
        const imgCount = paragraph.getElementsByTagName("img").length;
        const embedCount = paragraph.getElementsByTagName("embed").length;
        const objectCount = paragraph.getElementsByTagName("object").length;
        // At this point, nasty iframes have been removed, only remain embedded video ones.
        const iframeCount = paragraph.getElementsByTagName("iframe").length;
        const totalCount = imgCount + embedCount + objectCount + iframeCount;

        return totalCount === 0 && !this._getInnerText(paragraph, false);
      },
    );

    this._forEachNode(
      this._getAllNodesWithTag(articleContent, ["br"]),
      function (br) {
        const next = this._nextNode(br.nextSibling);
        if (next && next.tagName == "P") {
          br.parentNode.removeChild(br);
        }
      },
    );

    // Remove single-cell tables
    this._forEachNode(
      this._getAllNodesWithTag(articleContent, ["table"]),
      function (table) {
        const tbody = this._hasSingleTagInsideElement(table, "TBODY")
          ? table.firstElementChild
          : table;
        if (this._hasSingleTagInsideElement(tbody, "TR")) {
          const row = tbody.firstElementChild;
          if (this._hasSingleTagInsideElement(row, "TD")) {
            let cell = row.firstElementChild;
            cell = this._setNodeTag(
              cell,
              this._everyNode(cell.childNodes, this._isPhrasingContent)
                ? "P"
                : "DIV",
            );
            table.parentNode.replaceChild(cell, table);
          }
        }
      },
    );
  },

  /**
   * Initialize a node with the readability object. Also checks the
   * className/id for special names to add to its score.
   *
   * @param Element
   * @return void
   */
  _initializeNode: function (node) {
    node.readability = { "contentScore": 0 };

    switch (node.tagName) {
      case "DIV":
        node.readability.contentScore += 5;
        break;

      case "PRE":
      case "TD":
      case "BLOCKQUOTE":
        node.readability.contentScore += 3;
        break;

      case "ADDRESS":
      case "OL":
      case "UL":
      case "DL":
      case "DD":
      case "DT":
      case "LI":
      case "FORM":
        node.readability.contentScore -= 3;
        break;

      case "H1":
      case "H2":
      case "H3":
      case "H4":
      case "H5":
      case "H6":
      case "TH":
        node.readability.contentScore -= 5;
        break;
    }

    node.readability.contentScore += this._getClassWeight(node);
  },

  _removeAndGetNext: function (node) {
    const nextNode = this._getNextNode(node, true);
    node.parentNode.removeChild(node);
    return nextNode;
  },

  /**
   * Traverse the DOM from node to node, starting at the node passed in.
   * Pass true for the second parameter to indicate this node itself
   * (and its kids) are going away, and we want the next node over.
   *
   * Calling this in a loop will traverse the DOM depth-first.
   */
  _getNextNode: function (node, ignoreSelfAndKids) {
    // First check for kids if those aren't being ignored
    if (!ignoreSelfAndKids && node.firstElementChild) {
      return node.firstElementChild;
    }
    // Then for siblings...
    if (node.nextElementSibling) {
      return node.nextElementSibling;
    }
    // And finally, move up the parent chain *and* find a sibling
    // (because this is depth-first traversal, we will have already
    // seen the parent nodes themselves).
    do {
      node = node.parentNode;
    } while (node && !node.nextElementSibling);
    return node && node.nextElementSibling;
  },

  // compares second text to first one
  // 1 = same text, 0 = completely different text
  // works the way that it splits both texts into words and then finds words that are unique in second text
  // the result is given by the lower length of unique parts
  _textSimilarity: function (textA, textB) {
    const tokensA = textA.toLowerCase().split(this.REGEXPS.tokenize).filter(
      Boolean,
    );
    const tokensB = textB.toLowerCase().split(this.REGEXPS.tokenize).filter(
      Boolean,
    );
    if (!tokensA.length || !tokensB.length) {
      return 0;
    }
    const uniqTokensB = tokensB.filter((token) => !tokensA.includes(token));
    const distanceB = uniqTokensB.join(" ").length / tokensB.join(" ").length;
    return 1 - distanceB;
  },

  _checkByline: function (node, matchString) {
    if (this._articleByline) {
      return false;
    }

    let rel;
    let itemprop;
    if (node.getAttribute !== undefined) {
      rel = node.getAttribute("rel");
      itemprop = node.getAttribute("itemprop");
    }

    if (
      (rel === "author" || (itemprop && itemprop.indexOf("author") !== -1) ||
        this.REGEXPS.byline.test(matchString)) &&
      this._isValidByline(node.textContent)
    ) {
      this._articleByline = node.textContent.trim();
      return true;
    }

    return false;
  },

  _getNodeAncestors: function (node, maxDepth) {
    maxDepth = maxDepth || 0;
    let i = 0
    const ancestors = [];
    while (node.parentNode) {
      ancestors.push(node.parentNode);
      if (maxDepth && ++i === maxDepth) {
        break;
      }
      node = node.parentNode;
    }
    return ancestors;
  },

  /***
   * grabArticle - Using a constiety of metrics (content score, classname, element types), find the content that is
   *         most likely to be the stuff a user wants to read. Then return it wrapped up in a div.
   *
   * @param page a document to run upon. Needs to be a full document, complete with body.
   * @return Element
   */
  _grabArticle: function (page) {
    this.log("**** grabArticle ****");
    const doc = this._doc;
    const isPaging = page !== null;
    page = page ? page : this._doc.body;

    // We can't grab an article if we don't have a page!
    if (!page) {
      this.log("No body found in document. Abort.");
      return null;
    }

    const pageCacheHtml = page.innerHTML;

    while (true) {
      this.log("Starting grabArticle loop");
      const stripUnlikelyCandidates = this._flagIsActive(
        this.FLAG_STRIP_UNLIKELYS,
      );

      // First, node prepping. Trash nodes that look cruddy (like ones with the
      // class name "comment", etc), and turn divs into P tags where they have been
      // used inappropriately (as in, where they contain no other block level elements.)
      const elementsToScore = [];
      let node = this._doc.documentElement;

      let shouldRemoveTitleHeader = true;

      while (node) {
        if (node.tagName === "HTML") {
          this._articleLang = node.getAttribute("lang");
        }

        const matchString = node.className + " " + node.id;

        if (!this._isProbablyVisible(node)) {
          this.log("Removing hidden node - " + matchString);
          node = this._removeAndGetNext(node);
          continue;
        }

        // User is not able to see elements applied with both "aria-modal = true" and "role = dialog"
        if (
          node.getAttribute("aria-modal") == "true" &&
          node.getAttribute("role") == "dialog"
        ) {
          node = this._removeAndGetNext(node);
          continue;
        }

        // Check to see if this node is a byline, and remove it if it is.
        if (this._checkByline(node, matchString)) {
          node = this._removeAndGetNext(node);
          continue;
        }

        if (shouldRemoveTitleHeader && this._headerDuplicatesTitle(node)) {
          this.log(
            "Removing header: ",
            node.textContent.trim(),
            this._articleTitle.trim(),
          );
          shouldRemoveTitleHeader = false;
          node = this._removeAndGetNext(node);
          continue;
        }

        // Remove unlikely candidates
        if (stripUnlikelyCandidates) {
          if (
            this.REGEXPS.unlikelyCandidates.test(matchString) &&
            !this.REGEXPS.okMaybeItsACandidate.test(matchString) &&
            !this._hasAncestorTag(node, "table") &&
            !this._hasAncestorTag(node, "code") &&
            node.tagName !== "BODY" &&
            node.tagName !== "A"
          ) {
            this.log("Removing unlikely candidate - " + matchString);
            node = this._removeAndGetNext(node);
            continue;
          }

          if (this.UNLIKELY_ROLES.includes(node.getAttribute("role"))) {
            this.log(
              "Removing content with role " + node.getAttribute("role") +
                " - " + matchString,
            );
            node = this._removeAndGetNext(node);
            continue;
          }
        }

        // Remove DIV, SECTION, and HEADER nodes without any content(e.g. text, image, video, or iframe).
        if (
          (node.tagName === "DIV" || node.tagName === "SECTION" ||
            node.tagName === "HEADER" ||
            node.tagName === "H1" || node.tagName === "H2" ||
            node.tagName === "H3" ||
            node.tagName === "H4" || node.tagName === "H5" ||
            node.tagName === "H6") &&
          this._isElementWithoutContent(node)
        ) {
          node = this._removeAndGetNext(node);
          continue;
        }

        if (this.DEFAULT_TAGS_TO_SCORE.indexOf(node.tagName) !== -1) {
          elementsToScore.push(node);
        }

        // Turn all divs that don't have children block level elements into p's
        if (node.tagName === "DIV") {
          // Put phrasing content into paragraphs.
          let p = null;
          let childNode = node.firstChild;
          while (childNode) {
            const nextSibling = childNode.nextSibling;
            if (this._isPhrasingContent(childNode)) {
              if (p !== null) {
                p.appendChild(childNode);
              } else if (!this._isWhitespace(childNode)) {
                p = doc.createElement("p");
                node.replaceChild(p, childNode);
                p.appendChild(childNode);
              }
            } else if (p !== null) {
              while (p.lastChild && this._isWhitespace(p.lastChild)) {
                p.removeChild(p.lastChild);
              }
              p = null;
            }
            childNode = nextSibling;
          }

          // Sites like http://mobile.slate.com encloses each paragraph with a DIV
          // element. DIVs with only a P element inside and no text content can be
          // safely converted into plain P elements to avoid confusing the scoring
          // algorithm with DIVs with are, in practice, paragraphs.
          if (
            this._hasSingleTagInsideElement(node, "P") &&
            this._getLinkDensity(node) < 0.25
          ) {
            const newNode = node.children[0];
            node.parentNode.replaceChild(newNode, node);
            node = newNode;
            elementsToScore.push(node);
          } else if (!this._hasChildBlockElement(node)) {
            node = this._setNodeTag(node, "P");
            elementsToScore.push(node);
          }
        }
        node = this._getNextNode(node);
      }

      /**
       * Loop through all paragraphs, and assign a score to them based on how content-y they look.
       * Then add their score to their parent node.
       *
       * A score is determined by things like number of commas, class names, etc. Maybe eventually link density.
       */
      const candidates = [];
      this._forEachNode(elementsToScore, function (elementToScore) {
        if (
          !elementToScore.parentNode ||
          typeof (elementToScore.parentNode.tagName) === "undefined"
        ) {
          return;
        }

        // If this paragraph is less than 25 characters, don't even count it.
        const innerText = this._getInnerText(elementToScore);
        if (innerText.length < 25) {
          return;
        }

        // Exclude nodes with no ancestor.
        const ancestors = this._getNodeAncestors(elementToScore, 5);
        if (ancestors.length === 0) {
          return;
        }

        let contentScore = 0;

        // Add a point for the paragraph itself as a base.
        contentScore += 1;

        // Add points for any commas within this paragraph.
        contentScore += innerText.split(this.REGEXPS.commas).length;

        // For every 100 characters in this paragraph, add another point. Up to 3 points.
        contentScore += Math.min(Math.floor(innerText.length / 100), 3);

        // Initialize and score ancestors.
        this._forEachNode(ancestors, function (ancestor, level) {
          if (
            !ancestor.tagName || !ancestor.parentNode ||
            typeof (ancestor.parentNode.tagName) === "undefined"
          ) {
            return;
          }

          if (typeof (ancestor.readability) === "undefined") {
            this._initializeNode(ancestor);
            candidates.push(ancestor);
          }

          // Node score divider:
          // - parent:             1 (no division)
          // - grandparent:        2
          // - great grandparent+: ancestor level * 3
          let scoreDivider;
          if (level === 0) {
            scoreDivider = 1;
          } else if (level === 1) {
            scoreDivider = 2;
          } else {
            scoreDivider = level * 3;
          }
          ancestor.readability.contentScore += contentScore / scoreDivider;
        });
      });

      // After we've calculated scores, loop through all of the possible
      // candidate nodes we found and find the one with the highest score.
      const topCandidates = [];
      for (let c = 0, cl = candidates.length; c < cl; c += 1) {
        const candidate = candidates[c];

        // Scale the final candidates score based on link density. Good content
        // should have a relatively small link density (5% or less) and be mostly
        // unaffected by this operation.
        const candidateScore = candidate.readability.contentScore *
          (1 - this._getLinkDensity(candidate));
        candidate.readability.contentScore = candidateScore;

        this.log("Candidate:", candidate, "with score " + candidateScore);

        for (let t = 0; t < this._nbTopCandidates; t++) {
          const aTopCandidate = topCandidates[t];

          if (
            !aTopCandidate ||
            candidateScore > aTopCandidate.readability.contentScore
          ) {
            topCandidates.splice(t, 0, candidate);
            if (topCandidates.length > this._nbTopCandidates) {
              topCandidates.pop();
            }
            break;
          }
        }
      }

      let topCandidate = topCandidates[0] || null;
      let neededToCreateTopCandidate = false;
      let parentOfTopCandidate;

      // If we still have no top candidate, just use the body as a last resort.
      // We also have to copy the body node so it is something we can modify.
      if (topCandidate === null || topCandidate.tagName === "BODY") {
        // Move all of the page's children into topCandidate
        topCandidate = doc.createElement("DIV");
        neededToCreateTopCandidate = true;
        // Move everything (not just elements, also text nodes etc.) into the container
        // so we even include text directly in the body:
        while (page.firstChild) {
          this.log("Moving child out:", page.firstChild);
          topCandidate.appendChild(page.firstChild);
        }

        page.appendChild(topCandidate);

        this._initializeNode(topCandidate);
      } else if (topCandidate) {
        // Find a better top candidate node if it contains (at least three) nodes which belong to `topCandidates` array
        // and whose scores are quite closed with current `topCandidate` node.
        const alternativeCandidateAncestors = [];
        for (let i = 1; i < topCandidates.length; i++) {
          if (
            topCandidates[i].readability.contentScore /
                topCandidate.readability.contentScore >= 0.75
          ) {
            alternativeCandidateAncestors.push(
              this._getNodeAncestors(topCandidates[i]),
            );
          }
        }
        const MINIMUM_TOPCANDIDATES = 3;
        if (alternativeCandidateAncestors.length >= MINIMUM_TOPCANDIDATES) {
          parentOfTopCandidate = topCandidate.parentNode;
          while (parentOfTopCandidate.tagName !== "BODY") {
            let listsContainingThisAncestor = 0;
            let ancestorIndex = 0;
            for (
              ancestorIndex < alternativeCandidateAncestors.length &&
              listsContainingThisAncestor < MINIMUM_TOPCANDIDATES;
              ancestorIndex++;
            ) {
              listsContainingThisAncestor += Number(
                alternativeCandidateAncestors[ancestorIndex].includes(
                  parentOfTopCandidate,
                ),
              );
            }
            if (listsContainingThisAncestor >= MINIMUM_TOPCANDIDATES) {
              topCandidate = parentOfTopCandidate;
              break;
            }
            parentOfTopCandidate = parentOfTopCandidate.parentNode;
          }
        }
        if (!topCandidate.readability) {
          this._initializeNode(topCandidate);
        }

        // Because of our bonus system, parents of candidates might have scores
        // themselves. They get half of the node. There won't be nodes with higher
        // scores than our topCandidate, but if we see the score going *up* in the first
        // few steps up the tree, that's a decent sign that there might be more content
        // lurking in other places that we want to unify in. The sibling stuff
        // below does some of that - but only if we've looked high enough up the DOM
        // tree.
        parentOfTopCandidate = topCandidate.parentNode;
        let lastScore = topCandidate.readability.contentScore;
        // The scores shouldn't get too low.
        const scoreThreshold = lastScore / 3;
        while (parentOfTopCandidate.tagName !== "BODY") {
          if (!parentOfTopCandidate.readability) {
            parentOfTopCandidate = parentOfTopCandidate.parentNode;
            continue;
          }
          const parentScore = parentOfTopCandidate.readability.contentScore;
          if (parentScore < scoreThreshold) {
            break;
          }
          if (parentScore > lastScore) {
            // Alright! We found a better parent to use.
            topCandidate = parentOfTopCandidate;
            break;
          }
          lastScore = parentOfTopCandidate.readability.contentScore;
          parentOfTopCandidate = parentOfTopCandidate.parentNode;
        }

        // If the top candidate is the only child, use parent instead. This will help sibling
        // joining logic when adjacent content is actually located in parent's sibling node.
        parentOfTopCandidate = topCandidate.parentNode;
        while (
          parentOfTopCandidate.tagName != "BODY" &&
          parentOfTopCandidate.children.length == 1
        ) {
          topCandidate = parentOfTopCandidate;
          parentOfTopCandidate = topCandidate.parentNode;
        }
        if (!topCandidate.readability) {
          this._initializeNode(topCandidate);
        }
      }

      // Now that we have the top candidate, look through its siblings for content
      // that might also be related. Things like preambles, content split by ads
      // that we removed, etc.
      let articleContent = doc.createElement("DIV");
      if (isPaging) {
        articleContent.id = "readability-content";
      }

      const siblingScoreThreshold = Math.max(
        10,
        topCandidate.readability.contentScore * 0.2,
      );
      // Keep potential top candidate's parent node to try to get text direction of it later.
      parentOfTopCandidate = topCandidate.parentNode;
      let siblings = parentOfTopCandidate.children;

      for (let s = 0, sl = siblings.length; s < sl; s++) {
        let sibling = siblings[s];
        let append = false;

        this.log(
          "Looking at sibling node:",
          sibling,
          sibling.readability
            ? ("with score " + sibling.readability.contentScore)
            : "",
        );
        this.log(
          "Sibling has score",
          sibling.readability ? sibling.readability.contentScore : "Unknown",
        );

        if (sibling === topCandidate) {
          append = true;
        } else {
          let contentBonus = 0;

          // Give a bonus if sibling nodes and top candidates have the example same classname
          if (
            sibling.className === topCandidate.className &&
            topCandidate.className !== ""
          ) {
            contentBonus += topCandidate.readability.contentScore * 0.2;
          }

          if (
            sibling.readability &&
            ((sibling.readability.contentScore + contentBonus) >=
              siblingScoreThreshold)
          ) {
            append = true;
          } else if (sibling.nodeName === "P") {
            const linkDensity = this._getLinkDensity(sibling);
            const nodeContent = this._getInnerText(sibling);
            const nodeLength = nodeContent.length;

            if (nodeLength > 80 && linkDensity < 0.25) {
              append = true;
            } else if (
              nodeLength < 80 && nodeLength > 0 && linkDensity === 0 &&
              nodeContent.search(/\.( |$)/) !== -1
            ) {
              append = true;
            }
          }
        }

        if (append) {
          this.log("Appending node:", sibling);

          if (this.ALTER_TO_DIV_EXCEPTIONS.indexOf(sibling.nodeName) === -1) {
            // We have a node that isn't a common block level element, like a form or td tag.
            // Turn it into a div so it doesn't get filtered out later by accident.
            this.log("Altering sibling:", sibling, "to div.");

            sibling = this._setNodeTag(sibling, "DIV");
          }

          articleContent.appendChild(sibling);
          // Fetch children again to make it compatible
          // with DOM parsers without live collection support.
          siblings = parentOfTopCandidate.children;
          // siblings is a reference to the children array, and
          // sibling is removed from the array when we call appendChild().
          // As a result, we must revisit this index since the nodes
          // have been shifted.
          s -= 1;
          sl -= 1;
        }
      }

      if (this._debug) {
        this.log("Article content pre-prep: " + articleContent.innerHTML);
      }
      // So we have all of the content that we need. Now we clean it up for presentation.
      this._prepArticle(articleContent);
      if (this._debug) {
        this.log("Article content post-prep: " + articleContent.innerHTML);
      }

      if (neededToCreateTopCandidate) {
        // We already created a fake div thing, and there wouldn't have been any siblings left
        // for the previous loop, so there's no point trying to create a new div, and then
        // move all the children over. Just assign IDs and class names here. No need to append
        // because that already happened anyway.
        topCandidate.id = "readability-page-1";
        topCandidate.className = "page";
      } else {
        const div = doc.createElement("DIV");
        div.id = "readability-page-1";
        div.className = "page";
        while (articleContent.firstChild) {
          div.appendChild(articleContent.firstChild);
        }
        articleContent.appendChild(div);
      }

      if (this._debug) {
        this.log("Article content after paging: " + articleContent.innerHTML);
      }

      let parseSuccessful = true;

      // Now that we've gone through the full algorithm, check to see if
      // we got any meaningful content. If we didn't, we may need to re-run
      // grabArticle with different flags set. This gives us a higher likelihood of
      // finding the content, and the sieve approach gives us a higher likelihood of
      // finding the -right- content.
      const textLength = this._getInnerText(articleContent, true).length;
      if (textLength < this._charThreshold) {
        parseSuccessful = false;
        page.innerHTML = pageCacheHtml;

        if (this._flagIsActive(this.FLAG_STRIP_UNLIKELYS)) {
          this._removeFlag(this.FLAG_STRIP_UNLIKELYS);
          this._attempts.push({
            articleContent: articleContent,
            textLength: textLength,
          });
        } else if (this._flagIsActive(this.FLAG_WEIGHT_CLASSES)) {
          this._removeFlag(this.FLAG_WEIGHT_CLASSES);
          this._attempts.push({
            articleContent: articleContent,
            textLength: textLength,
          });
        } else if (this._flagIsActive(this.FLAG_CLEAN_CONDITIONALLY)) {
          this._removeFlag(this.FLAG_CLEAN_CONDITIONALLY);
          this._attempts.push({
            articleContent: articleContent,
            textLength: textLength,
          });
        } else {
          this._attempts.push({
            articleContent: articleContent,
            textLength: textLength,
          });
          // No luck after removing flags, just return the longest text we found during the different loops
          this._attempts.sort(function (a, b) {
            return b.textLength - a.textLength;
          });

          // But first check if we actually have something
          if (!this._attempts[0].textLength) {
            return null;
          }

          articleContent = this._attempts[0].articleContent;
          parseSuccessful = true;
        }
      }

      if (parseSuccessful) {
        // Find out text direction from ancestors of final top candidate.
        const ancestors = [parentOfTopCandidate, topCandidate].concat(
          this._getNodeAncestors(parentOfTopCandidate),
        );
        this._someNode(ancestors, function (ancestor) {
          if (!ancestor.tagName) {
            return false;
          }
          const articleDir = ancestor.getAttribute("dir");
          if (articleDir) {
            this._articleDir = articleDir;
            return true;
          }
          return false;
        });
        return articleContent;
      }
    }
  },

  /**
   * Check whether the input string could be a byline.
   * This verifies that the input is a string, and that the length
   * is less than 100 chars.
   *
   * @param possibleByline {string} - a string to check whether its a byline.
   * @return Boolean - whether the input string is a byline.
   */
  _isValidByline: function (byline) {
    if (typeof byline == "string" || byline instanceof String) {
      byline = byline.trim();
      return (byline.length > 0) && (byline.length < 100);
    }
    return false;
  },

  /**
   * Converts some of the common HTML entities in string to their corresponding characters.
   *
   * @param str {string} - a string to unescape.
   * @return string without HTML entity.
   */
  _unescapeHtmlEntities: function (str) {
    if (!str) {
      return str;
    }

    const htmlEscapeMap = this.HTML_ESCAPE_MAP;
    return str.replace(/&(quot|amp|apos|lt|gt);/g, function (_, tag) {
      return htmlEscapeMap[tag];
    }).replace(
      /&#(?:x([0-9a-z]{1,4})|([0-9]{1,4}));/gi,
      function (_, hex, numStr) {
        const num = parseInt(hex || numStr, hex ? 16 : 10);
        return String.fromCharCode(num);
      },
    );
  },

  /**
   * Try to extract metadata from JSON-LD object.
   * For now, only Schema.org objects of type Article or its subtypes are supported.
   * @return Object with any metadata that could be extracted (possibly none)
   */
  _getJSONLD: function (doc) {
    const scripts = this._getAllNodesWithTag(doc, ["script"]);

    let metadata;

    this._forEachNode(scripts, function (jsonLdElement) {
      if (
        !metadata &&
        jsonLdElement.getAttribute("type") === "application/ld+json"
      ) {
        try {
          // Strip CDATA markers if present
          const content = jsonLdElement.textContent.replace(
            /^\s*<!\[CDATA\[|\]\]>\s*$/g,
            "",
          );
          let parsed = JSON.parse(content);
          if (
            !parsed["@context"] ||
            !parsed["@context"].match(/^https?\:\/\/schema\.org\/?$/)
          ) {
            return;
          }

          if (!parsed["@type"] && Array.isArray(parsed["@graph"])) {
            parsed = parsed["@graph"].find(function (it) {
              return (it["@type"] || "").match(
                this.REGEXPS.jsonLdArticleTypes,
              );
            });
          }

          if (
            !parsed ||
            !parsed["@type"] ||
            !parsed["@type"].match(this.REGEXPS.jsonLdArticleTypes)
          ) {
            return;
          }

          metadata = {};

          if (
            typeof parsed.name === "string" &&
            typeof parsed.headline === "string" &&
            parsed.name !== parsed.headline
          ) {
            // we have both name and headline element in the JSON-LD. They should both be the same but some websites like aktualne.cz
            // put their own name into "name" and the article title to "headline" which confuses Readability. So we try to check if either
            // "name" or "headline" closely matches the html title, and if so, use that one. If not, then we use "name" by default.

            const title = this._getArticleTitle();
            const nameMatches = this._textSimilarity(parsed.name, title) > 0.75;
            const headlineMatches =
              this._textSimilarity(parsed.headline, title) > 0.75;

            if (headlineMatches && !nameMatches) {
              metadata.title = parsed.headline;
            } else {
              metadata.title = parsed.name;
            }
          } else if (typeof parsed.name === "string") {
            metadata.title = parsed.name.trim();
          } else if (typeof parsed.headline === "string") {
            metadata.title = parsed.headline.trim();
          }
          if (parsed.author) {
            if (typeof parsed.author.name === "string") {
              metadata.byline = parsed.author.name.trim();
            } else if (
              Array.isArray(parsed.author) && parsed.author[0] &&
              typeof parsed.author[0].name === "string"
            ) {
              metadata.byline = parsed.author
                .filter(function (author) {
                  return author && typeof author.name === "string";
                })
                .map(function (author) {
                  return author.name.trim();
                })
                .join(", ");
            }
          }
          if (typeof parsed.description === "string") {
            metadata.excerpt = parsed.description.trim();
          }
          if (
            parsed.publisher &&
            typeof parsed.publisher.name === "string"
          ) {
            metadata.siteName = parsed.publisher.name.trim();
          }
          if (typeof parsed.datePublished === "string") {
            metadata.datePublished = parsed.datePublished.trim();
          }
          return;
        } catch (err) {
          this.log(err.message);
        }
      }
    });
    return metadata ? metadata : {};
  },

  /**
   * Attempts to get excerpt and byline metadata for the article.
   *
   * @param {Object} jsonld — object containing any metadata that
   * could be extracted from JSON-LD object.
   *
   * @return Object with optional "excerpt" and "byline" properties
   */
  _getArticleMetadata: function (jsonld) {
    const metadata = {};
    const values = {};
    const metaElements = this._doc.getElementsByTagName("meta");

    // property is a space-separated list of values
    const propertyPattern =
      /\s*(article|dc|dcterm|og|twitter)\s*:\s*(author|creator|description|published_time|title|site_name)\s*/gi;

    // name is a single value
    const namePattern =
      /^\s*(?:(dc|dcterm|og|twitter|weibo:(article|webpage))\s*[\.:]\s*)?(author|creator|description|title|site_name)\s*$/i;

    // Find description tags.
    this._forEachNode(metaElements, function (element) {
      const elementName = element.getAttribute("name");
      const elementProperty = element.getAttribute("property");
      const content = element.getAttribute("content");
      if (!content) {
        return;
      }
      let matches = null;
      let name = null;

      if (elementProperty) {
        matches = elementProperty.match(propertyPattern);
        if (matches) {
          // Convert to lowercase, and remove any whitespace
          // so we can match below.
          name = matches[0].toLowerCase().replace(/\s/g, "");
          // multiple authors
          values[name] = content.trim();
        }
      }
      if (!matches && elementName && namePattern.test(elementName)) {
        name = elementName;
        if (content) {
          // Convert to lowercase, remove any whitespace, and convert dots
          // to colons so we can match below.
          name = name.toLowerCase().replace(/\s/g, "").replace(/\./g, ":");
          values[name] = content.trim();
        }
      }
    });

    // get title
    metadata.title = jsonld.title ||
      values["dc:title"] ||
      values["dcterm:title"] ||
      values["og:title"] ||
      values["weibo:article:title"] ||
      values["weibo:webpage:title"] ||
      values["title"] ||
      values["twitter:title"];

    if (!metadata.title) {
      metadata.title = this._getArticleTitle();
    }

    // get author
    metadata.byline = jsonld.byline ||
      values["dc:creator"] ||
      values["dcterm:creator"] ||
      values["author"];

    // get description
    metadata.excerpt = jsonld.excerpt ||
      values["dc:description"] ||
      values["dcterm:description"] ||
      values["og:description"] ||
      values["weibo:article:description"] ||
      values["weibo:webpage:description"] ||
      values["description"] ||
      values["twitter:description"];

    // get site name
    metadata.siteName = jsonld.siteName ||
      values["og:site_name"];

    // get article published time
    metadata.publishedTime = jsonld.datePublished ||
      values["article:published_time"] || null;

    // in many sites the meta value is escaped with HTML entities,
    // so here we need to unescape it
    metadata.title = this._unescapeHtmlEntities(metadata.title);
    metadata.byline = this._unescapeHtmlEntities(metadata.byline);
    metadata.excerpt = this._unescapeHtmlEntities(metadata.excerpt);
    metadata.siteName = this._unescapeHtmlEntities(metadata.siteName);
    metadata.publishedTime = this._unescapeHtmlEntities(metadata.publishedTime);

    return metadata;
  },

  /**
   * Check if node is image, or if node contains exactly only one image
   * whether as a direct child or as its descendants.
   *
   * @param Element
   */
  _isSingleImage: function (node) {
    if (node.tagName === "IMG") {
      return true;
    }

    if (node.children.length !== 1 || node.textContent.trim() !== "") {
      return false;
    }

    return this._isSingleImage(node.children[0]);
  },

  /**
   * Find all <noscript> that are located after <img> nodes, and which contain only one
   * <img> element. Replace the first image with the image from inside the <noscript> tag,
   * and remove the <noscript> tag. This improves the quality of the images we use on
   * some sites (e.g. Medium).
   *
   * @param Element
   */
  _unwrapNoscriptImages: function (doc) {
    // Find img without source or attributes that might contains image, and remove it.
    // This is done to prevent a placeholder img is replaced by img from noscript in next step.
    const imgs = Array.from(doc.getElementsByTagName("img"));
    this._forEachNode(imgs, function (img) {
      for (let i = 0; i < img.attributes.length; i++) {
        const attr = img.attributes[i];
        switch (attr.name) {
          case "src":
          case "srcset":
          case "data-src":
          case "data-srcset":
            return;
        }

        if (/\.(jpg|jpeg|png|webp)/i.test(attr.value)) {
          return;
        }
      }

      img.parentNode.removeChild(img);
    });

    // Next find noscript and try to extract its image
    const noscripts = Array.from(doc.getElementsByTagName("noscript"));
    this._forEachNode(noscripts, function (noscript) {
      // Parse content of noscript and make sure it only contains image
      const tmp = doc.createElement("div");
      tmp.innerHTML = noscript.innerHTML;
      if (!this._isSingleImage(tmp)) {
        return;
      }

      // If noscript has previous sibling and it only contains image,
      // replace it with noscript content. However we also keep old
      // attributes that might contains image.
      const prevElement = noscript.previousElementSibling;
      if (prevElement && this._isSingleImage(prevElement)) {
        let prevImg = prevElement;
        if (prevImg.tagName !== "IMG") {
          prevImg = prevElement.getElementsByTagName("img")[0];
        }

        const newImg = tmp.getElementsByTagName("img")[0];
        for (let i = 0; i < prevImg.attributes.length; i++) {
          const attr = prevImg.attributes[i];
          if (attr.value === "") {
            continue;
          }

          if (
            attr.name === "src" || attr.name === "srcset" ||
            /\.(jpg|jpeg|png|webp)/i.test(attr.value)
          ) {
            if (newImg.getAttribute(attr.name) === attr.value) {
              continue;
            }

            let attrName = attr.name;
            if (newImg.hasAttribute(attrName)) {
              attrName = "data-old-" + attrName;
            }

            newImg.setAttribute(attrName, attr.value);
          }
        }

        noscript.parentNode.replaceChild(tmp.firstElementChild, prevElement);
      }
    });
  },

  /**
   * Removes script tags from the document.
   *
   * @param Element
   */
  _removeScripts: function (doc) {
    this._removeNodes(this._getAllNodesWithTag(doc, ["script", "noscript"]));
  },

  /**
   * Check if this node has only whitespace and a single element with given tag
   * Returns false if the DIV node contains non-empty text nodes
   * or if it contains no element with given tag or more than 1 element.
   *
   * @param Element
   * @param string tag of child element
   */
  _hasSingleTagInsideElement: function (element, tag) {
    // There should be exactly 1 element child with given tag
    if (element.children.length != 1 || element.children[0].tagName !== tag) {
      return false;
    }

    // And there should be no text nodes with real content
    return !this._someNode(element.childNodes, function (node) {
      return node.nodeType === this.TEXT_NODE &&
        this.REGEXPS.hasContent.test(node.textContent);
    });
  },

  _isElementWithoutContent: function (node) {
    return node.nodeType === this.ELEMENT_NODE &&
      node.textContent.trim().length == 0 &&
      (node.children.length == 0 ||
        node.children.length ==
          node.getElementsByTagName("br").length +
            node.getElementsByTagName("hr").length);
  },

  /**
   * Determine whether element has any children block level elements.
   *
   * @param Element
   */
  _hasChildBlockElement: function (element) {
    return this._someNode(element.childNodes, function (node) {
      return this.DIV_TO_P_ELEMS.has(node.tagName) ||
        this._hasChildBlockElement(node);
    });
  },

  /***
   * Determine if a node qualifies as phrasing content.
   * https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Content_categories#Phrasing_content
   */
  _isPhrasingContent: function (node) {
    return node.nodeType === this.TEXT_NODE ||
      this.PHRASING_ELEMS.indexOf(node.tagName) !== -1 ||
      ((node.tagName === "A" || node.tagName === "DEL" ||
        node.tagName === "INS") &&
        this._everyNode(node.childNodes, this._isPhrasingContent));
  },

  _isWhitespace: function (node) {
    return (node.nodeType === this.TEXT_NODE &&
      node.textContent.trim().length === 0) ||
      (node.nodeType === this.ELEMENT_NODE && node.tagName === "BR");
  },

  /**
   * Get the inner text of a node - cross browser compatibly.
   * This also strips out any excess whitespace to be found.
   *
   * @param Element
   * @param Boolean normalizeSpaces (default: true)
   * @return string
   */
  _getInnerText: function (e, normalizeSpaces) {
    normalizeSpaces = (typeof normalizeSpaces === "undefined")
      ? true
      : normalizeSpaces;
    const textContent = e.textContent.trim();

    if (normalizeSpaces) {
      return textContent.replace(this.REGEXPS.normalize, " ");
    }
    return textContent;
  },

  /**
   * Get the number of times a string s appears in the node e.
   *
   * @param Element
   * @param string - what to split on. Default is ","
   * @return number (integer)
   */
  _getCharCount: function (e, s) {
    s = s || ",";
    return this._getInnerText(e).split(s).length - 1;
  },

  /**
   * Remove the style attribute on every e and under.
   * TODO: Test if getElementsByTagName(*) is faster.
   *
   * @param Element
   * @return void
   */
  _cleanStyles: function (e) {
    if (!e || e.tagName.toLowerCase() === "svg") {
      return;
    }

    // Remove `style` and deprecated presentational attributes
    for (let i = 0; i < this.PRESENTATIONAL_ATTRIBUTES.length; i++) {
      e.removeAttribute(this.PRESENTATIONAL_ATTRIBUTES[i]);
    }

    if (this.DEPRECATED_SIZE_ATTRIBUTE_ELEMS.indexOf(e.tagName) !== -1) {
      e.removeAttribute("width");
      e.removeAttribute("height");
    }

    let cur = e.firstElementChild;
    while (cur !== null) {
      this._cleanStyles(cur);
      cur = cur.nextElementSibling;
    }
  },

  /**
   * Get the density of links as a percentage of the content
   * This is the amount of text that is inside a link divided by the total text in the node.
   *
   * @param Element
   * @return number (float)
   */
  _getLinkDensity: function (element) {
    const textLength = this._getInnerText(element).length;
    if (textLength === 0) {
      return 0;
    }

    let linkLength = 0;

    // XXX implement _reduceNodeList?
    this._forEachNode(element.getElementsByTagName("a"), function (linkNode) {
      const href = linkNode.getAttribute("href");
      const coefficient = href && this.REGEXPS.hashUrl.test(href) ? 0.3 : 1;
      linkLength += this._getInnerText(linkNode).length * coefficient;
    });

    return linkLength / textLength;
  },

  /**
   * Get an elements class/id weight. Uses regular expressions to tell if this
   * element looks good or bad.
   *
   * @param Element
   * @return number (Integer)
   */
  _getClassWeight: function (e) {
    if (!this._flagIsActive(this.FLAG_WEIGHT_CLASSES)) {
      return 0;
    }

    let weight = 0;

    // Look for a special classname
    if (typeof (e.className) === "string" && e.className !== "") {
      if (this.REGEXPS.negative.test(e.className)) {
        weight -= 25;
      }

      if (this.REGEXPS.positive.test(e.className)) {
        weight += 25;
      }
    }

    // Look for a special ID
    if (typeof (e.id) === "string" && e.id !== "") {
      if (this.REGEXPS.negative.test(e.id)) {
        weight -= 25;
      }

      if (this.REGEXPS.positive.test(e.id)) {
        weight += 25;
      }
    }

    return weight;
  },

  /**
   * Clean a node of all elements of type "tag".
   * (Unless it's a youtube/vimeo video. People love movies.)
   *
   * @param Element
   * @param string tag to clean
   * @return void
   */
  _clean: function (e, tag) {
    const isEmbed = ["object", "embed", "iframe"].indexOf(tag) !== -1;

    this._removeNodes(this._getAllNodesWithTag(e, [tag]), function (element) {
      // Allow youtube and vimeo videos through as people usually want to see those.
      if (isEmbed) {
        // First, check the elements attributes to see if any of them contain youtube or vimeo
        for (let i = 0; i < element.attributes.length; i++) {
          if (this._allowedVideoRegex.test(element.attributes[i].value)) {
            return false;
          }
        }

        // For embed with <object> tag, check inner HTML as well.
        if (
          element.tagName === "object" &&
          this._allowedVideoRegex.test(element.innerHTML)
        ) {
          return false;
        }
      }

      return true;
    });
  },

  /**
   * Check if a given node has one of its ancestor tag name matching the
   * provided one.
   * @param  HTMLElement node
   * @param  String      tagName
   * @param  Number      maxDepth
   * @param  Function    filterFn a filter to invoke to determine whether this node 'counts'
   * @return Boolean
   */
  _hasAncestorTag: function (node, tagName, maxDepth, filterFn) {
    maxDepth = maxDepth || 3;
    tagName = tagName.toUpperCase();
    let depth = 0;
    while (node.parentNode) {
      if (maxDepth > 0 && depth > maxDepth) {
        return false;
      }
      if (
        node.parentNode.tagName === tagName &&
        (!filterFn || filterFn(node.parentNode))
      ) {
        return true;
      }
      node = node.parentNode;
      depth++;
    }
    return false;
  },

  /**
   * Return an object indicating how many rows and columns this table has.
   */
  _getRowAndColumnCount: function (table) {
    let rows = 0;
    let columns = 0;
    const trs = table.getElementsByTagName("tr");
    for (let i = 0; i < trs.length; i++) {
      let rowspan = trs[i].getAttribute("rowspan") || 0;
      if (rowspan) {
        rowspan = parseInt(rowspan, 10);
      }
      rows += rowspan || 1;

      // Now look for column-related info
      let columnsInThisRow = 0;
      const cells = trs[i].getElementsByTagName("td");
      for (let j = 0; j < cells.length; j++) {
        let colspan = cells[j].getAttribute("colspan") || 0;
        if (colspan) {
          colspan = parseInt(colspan, 10);
        }
        columnsInThisRow += colspan || 1;
      }
      columns = Math.max(columns, columnsInThisRow);
    }
    return { rows: rows, columns: columns };
  },

  /**
   * Look for 'data' (as opposed to 'layout') tables, for which we use
   * similar checks as
   * https://searchfox.org/mozilla-central/rev/f82d5c549f046cb64ce5602bfd894b7ae807c8f8/accessible/generic/TableAccessible.cpp#19
   */
  _markDataTables: function (root) {
    const tables = root.getElementsByTagName("table");
    for (let i = 0; i < tables.length; i++) {
      const table = tables[i];
      const role = table.getAttribute("role");
      if (role == "presentation") {
        table._readabilityDataTable = false;
        continue;
      }
      const datatable = table.getAttribute("datatable");
      if (datatable == "0") {
        table._readabilityDataTable = false;
        continue;
      }
      const summary = table.getAttribute("summary");
      if (summary) {
        table._readabilityDataTable = true;
        continue;
      }

      const caption = table.getElementsByTagName("caption")[0];
      if (caption && caption.childNodes.length > 0) {
        table._readabilityDataTable = true;
        continue;
      }

      // If the table has a descendant with any of these tags, consider a data table:
      const dataTableDescendants = ["col", "colgroup", "tfoot", "thead", "th"];
      const descendantExists = function (tag) {
        return !!table.getElementsByTagName(tag)[0];
      };
      if (dataTableDescendants.some(descendantExists)) {
        this.log("Data table because found data-y descendant");
        table._readabilityDataTable = true;
        continue;
      }

      // Nested tables indicate a layout table:
      if (table.getElementsByTagName("table")[0]) {
        table._readabilityDataTable = false;
        continue;
      }

      const sizeInfo = this._getRowAndColumnCount(table);
      if (sizeInfo.rows >= 10 || sizeInfo.columns > 4) {
        table._readabilityDataTable = true;
        continue;
      }
      // Now just go by size entirely:
      table._readabilityDataTable = sizeInfo.rows * sizeInfo.columns > 10;
    }
  },

  /* convert images and figures that have properties like data-src into images that can be loaded without JS */
  _fixLazyImages: function (root) {
    this._forEachNode(
      this._getAllNodesWithTag(root, ["img", "picture", "figure"]),
      function (elem) {
        // In some sites (e.g. Kotaku), they put 1px square image as base64 data uri in the src attribute.
        // So, here we check if the data uri is too short, just might as well remove it.
        if (elem.src && this.REGEXPS.b64DataUrl.test(elem.src)) {
          // Make sure it's not SVG, because SVG can have a meaningful image in under 133 bytes.
          const parts = this.REGEXPS.b64DataUrl.exec(elem.src);
          if (parts[1] === "image/svg+xml") {
            return;
          }

          // Make sure this element has other attributes which contains image.
          // If it doesn't, then this src is important and shouldn't be removed.
          let srcCouldBeRemoved = false;
          for (let i = 0; i < elem.attributes.length; i++) {
            const attr = elem.attributes[i];
            if (attr.name === "src") {
              continue;
            }

            if (/\.(jpg|jpeg|png|webp)/i.test(attr.value)) {
              srcCouldBeRemoved = true;
              break;
            }
          }

          // Here we assume if image is less than 100 bytes (or 133B after encoded to base64)
          // it will be too small, therefore it might be placeholder image.
          if (srcCouldBeRemoved) {
            const b64starts = elem.src.search(/base64\s*/i) + 7;
            const b64length = elem.src.length - b64starts;
            if (b64length < 133) {
              elem.removeAttribute("src");
            }
          }
        }

        // also check for "null" to work around https://github.com/jsdom/jsdom/issues/2580
        if (
          (elem.src || (elem.srcset && elem.srcset != "null")) &&
          elem.className.toLowerCase().indexOf("lazy") === -1
        ) {
          return;
        }

        let attr;
        for (let j = 0; j < elem.attributes.length; j++) {
          attr = elem.attributes[j];
          if (
            attr.name === "src" || attr.name === "srcset" || attr.name === "alt"
          ) {
            continue;
          }
          let copyTo = null;
          if (/\.(jpg|jpeg|png|webp)\s+\d/.test(attr.value)) {
            copyTo = "srcset";
          } else if (/^\s*\S+\.(jpg|jpeg|png|webp)\S*\s*$/.test(attr.value)) {
            copyTo = "src";
          }
          if (copyTo) {
            //if this is an img or picture, set the attribute directly
            if (elem.tagName === "IMG" || elem.tagName === "PICTURE") {
              elem.setAttribute(copyTo, attr.value);
            } else if (
              elem.tagName === "FIGURE" &&
              !this._getAllNodesWithTag(elem, ["img", "picture"]).length
            ) {
              //if the item is a <figure> that does not contain an image or picture, create one and place it inside the figure
              //see the nytimes-3 testcase for an example
              const img = this._doc.createElement("img");
              img.setAttribute(copyTo, attr.value);
              elem.appendChild(img);
            }
          }
        }
      },
    );
  },

  _getTextDensity: function (e, tags) {
    const textLength = this._getInnerText(e, true).length;
    if (textLength === 0) {
      return 0;
    }
    let childrenLength = 0;
    const children = this._getAllNodesWithTag(e, tags);
    this._forEachNode(
      children,
      (child) => childrenLength += this._getInnerText(child, true).length,
    );
    return childrenLength / textLength;
  },

  /**
   * Clean an element of all tags of type "tag" if they look fishy.
   * "Fishy" is an algorithm based on content length, classnames, link density, number of images & embeds, etc.
   *
   * @return void
   */
  _cleanConditionally: function (e, tag) {
    if (!this._flagIsActive(this.FLAG_CLEAN_CONDITIONALLY)) {
      return;
    }

    // Gather counts for other typical elements embedded within.
    // Traverse backwards so we can remove nodes at the same time
    // without effecting the traversal.
    //
    // TODO: Consider taking into account original contentScore here.
    this._removeNodes(this._getAllNodesWithTag(e, [tag]), function (node) {
      // First check if this node IS data table, in which case don't remove it.
      const isDataTable = function (t) {
        return t._readabilityDataTable;
      };

      let isList = tag === "ul" || tag === "ol";
      if (!isList) {
        let listLength = 0;
        const listNodes = this._getAllNodesWithTag(node, ["ul", "ol"]);
        this._forEachNode(
          listNodes,
          (list) => listLength += this._getInnerText(list).length,
        );
        isList = listLength / this._getInnerText(node).length > 0.9;
      }

      if (tag === "table" && isDataTable(node)) {
        return false;
      }

      // Next check if we're inside a data table, in which case don't remove it as well.
      if (this._hasAncestorTag(node, "table", -1, isDataTable)) {
        return false;
      }

      if (this._hasAncestorTag(node, "code")) {
        return false;
      }

      const weight = this._getClassWeight(node);

      this.log("Cleaning Conditionally", node);

      const contentScore = 0;

      if (weight + contentScore < 0) {
        return true;
      }

      if (this._getCharCount(node, ",") < 10) {
        // If there are not very many commas, and the number of
        // non-paragraph elements is more than paragraphs or other
        // ominous signs, remove the element.
        const p = node.getElementsByTagName("p").length;
        const img = node.getElementsByTagName("img").length;
        const li = node.getElementsByTagName("li").length - 100;
        const input = node.getElementsByTagName("input").length;
        const headingDensity = this._getTextDensity(node, [
          "h1",
          "h2",
          "h3",
          "h4",
          "h5",
          "h6",
        ]);

        let embedCount = 0;
        const embeds = this._getAllNodesWithTag(node, [
          "object",
          "embed",
          "iframe",
        ]);

        for (let i = 0; i < embeds.length; i++) {
          // If this embed has attribute that matches video regex, don't delete it.
          for (let j = 0; j < embeds[i].attributes.length; j++) {
            if (this._allowedVideoRegex.test(embeds[i].attributes[j].value)) {
              return false;
            }
          }

          // For embed with <object> tag, check inner HTML as well.
          if (
            embeds[i].tagName === "object" &&
            this._allowedVideoRegex.test(embeds[i].innerHTML)
          ) {
            return false;
          }

          embedCount++;
        }

        const linkDensity = this._getLinkDensity(node);
        const contentLength = this._getInnerText(node).length;

        const haveToRemove =
          (img > 1 && p / img < 0.5 && !this._hasAncestorTag(node, "figure")) ||
          (!isList && li > p) ||
          (input > Math.floor(p / 3)) ||
          (!isList && headingDensity < 0.9 && contentLength < 25 &&
            (img === 0 || img > 2) && !this._hasAncestorTag(node, "figure")) ||
          (!isList && weight < 25 && linkDensity > 0.2) ||
          (weight >= 25 && linkDensity > 0.5) ||
          ((embedCount === 1 && contentLength < 75) || embedCount > 1);
        // Allow simple lists of images to remain in pages
        if (isList && haveToRemove) {
          for (let x = 0; x < node.children.length; x++) {
            const child = node.children[x];
            // Don't filter in lists with li's that contain more than one child
            if (child.children.length > 1) {
              return haveToRemove;
            }
          }
          const li_count = node.getElementsByTagName("li").length;
          // Only allow the list to remain if every li contains an image
          if (img == li_count) {
            return false;
          }
        }
        return haveToRemove;
      }
      return false;
    });
  },

  /**
   * Clean out elements that match the specified conditions
   *
   * @param Element
   * @param Function determines whether a node should be removed
   * @return void
   */
  _cleanMatchedNodes: function (e, filter) {
    const endOfSearchMarkerNode = this._getNextNode(e, true);
    let next = this._getNextNode(e);
    while (next && next != endOfSearchMarkerNode) {
      if (filter.call(this, next, next.className + " " + next.id)) {
        next = this._removeAndGetNext(next);
      } else {
        next = this._getNextNode(next);
      }
    }
  },

  /**
   * Clean out spurious headers from an Element.
   *
   * @param Element
   * @return void
   */
  _cleanHeaders: function (e) {
    const headingNodes = this._getAllNodesWithTag(e, ["h1", "h2"]);
    this._removeNodes(headingNodes, function (node) {
      const shouldRemove = this._getClassWeight(node) < 0;
      if (shouldRemove) {
        this.log("Removing header with low class weight:", node);
      }
      return shouldRemove;
    });
  },

  /**
   * Check if this node is an H1 or H2 element whose content is mostly
   * the same as the article title.
   *
   * @param Element  the node to check.
   * @return boolean indicating whether this is a title-like header.
   */
  _headerDuplicatesTitle: function (node) {
    if (node.tagName != "H1" && node.tagName != "H2") {
      return false;
    }
    const heading = this._getInnerText(node, false);
    this.log("Evaluating similarity of header:", heading, this._articleTitle);
    return this._textSimilarity(this._articleTitle, heading) > 0.75;
  },

  _flagIsActive: function (flag) {
    return (this._flags & flag) > 0;
  },

  _removeFlag: function (flag) {
    this._flags = this._flags & ~flag;
  },

  _isProbablyVisible: function (node) {
    // Have to null-check node.style and node.className.indexOf to deal with SVG and MathML nodes.
    return (!node.style || node.style.display != "none") &&
      (!node.style || node.style.visibility != "hidden") &&
      !node.hasAttribute("hidden") &&
      //check for "fallback-image" so that wikimedia math images are displayed
      (!node.hasAttribute("aria-hidden") ||
        node.getAttribute("aria-hidden") != "true" ||
        (node.className && node.className.indexOf &&
          node.className.indexOf("fallback-image") !== -1));
  },

  /**
   * Runs readability.
   *
   * Workflow:
   *  1. Prep the document by removing script tags, css, etc.
   *  2. Build readability's DOM tree.
   *  3. Grab the article content from the current dom tree.
   *  4. Replace the current DOM tree with the new one.
   *  5. Read peacefully.
   *
   * @return void
   */
  parse: function () {
    // Avoid parsing too large documents, as per configuration option
    if (this._maxElemsToParse > 0) {
      const numTags = this._doc.getElementsByTagName("*").length;
      if (numTags > this._maxElemsToParse) {
        throw new Error(
          "Aborting parsing document; " + numTags + " elements found",
        );
      }
    }

    // Unwrap image from noscript
    this._unwrapNoscriptImages(this._doc);

    // Extract JSON-LD metadata before removing scripts
    const jsonLd = this._disableJSONLD ? {} : this._getJSONLD(this._doc);

    // Remove script tags from the document.
    this._removeScripts(this._doc);

    this._prepDocument();

    const metadata = this._getArticleMetadata(jsonLd);
    this._articleTitle = metadata.title;

    const articleContent = this._grabArticle();
    if (!articleContent) {
      return null;
    }

    this.log("Grabbed: " + articleContent.innerHTML);

    this._postProcessContent(articleContent);

    // If we haven't found an excerpt in the article's metadata, use the article's
    // first paragraph as the excerpt. This is used for displaying a preview of
    // the article's content.
    if (!metadata.excerpt) {
      const paragraphs = articleContent.getElementsByTagName("p");
      if (paragraphs.length > 0) {
        metadata.excerpt = paragraphs[0].textContent.trim();
      }
    }

    const textContent = articleContent.textContent;
    return {
      title: this._articleTitle,
      byline: metadata.byline || this._articleByline,
      dir: this._articleDir,
      lang: this._articleLang,
      content: this._serializer(articleContent),
      textContent: textContent,
      length: textContent.length,
      excerpt: metadata.excerpt,
      siteName: metadata.siteName || this._articleSiteName,
      publishedTime: metadata.publishedTime,
    };
  },
};

export default Readability;