turndown.js

var TurndownService = (function () {
  'use strict';

  function extend (destination) {
    for (var i = 1; i < arguments.length; i++) {
      var source = arguments[i];
      for (var key in source) {
        if (source.hasOwnProperty(key)) destination[key] = source[key];
      }
    }
    return destination
  }

  function repeat (character, count) {
    return Array(count + 1).join(character)
  }

  var blockElements = [
    'address', 'article', 'aside', 'audio', 'blockquote', 'body', 'canvas',
    'center', 'dd', 'dir', 'div', 'dl', 'dt', 'fieldset', 'figcaption',
    'figure', 'footer', 'form', 'frameset', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
    'header', 'hgroup', 'hr', 'html', 'isindex', 'li', 'main', 'menu', 'nav',
    'noframes', 'noscript', 'ol', 'output', 'p', 'pre', 'section', 'table',
    'tbody', 'td', 'tfoot', 'th', 'thead', 'tr', 'ul'
  ];

  function isBlock (node) {
    return blockElements.indexOf(node.nodeName.toLowerCase()) !== -1
  }

  var voidElements = [
    'area', 'base', 'br', 'col', 'command', 'embed', 'hr', 'img', 'input',
    'keygen', 'link', 'meta', 'param', 'source', 'track', 'wbr'
  ];

  function isVoid (node) {
    return voidElements.indexOf(node.nodeName.toLowerCase()) !== -1
  }

  var voidSelector = voidElements.join();
  function hasVoid (node) {
    return node.querySelector && node.querySelector(voidSelector)
  }

  var rules = {};

  rules.paragraph = {
    filter: 'p',

    replacement: function (content) {
      return '\n\n' + content + '\n\n'
    }
  };

  rules.lineBreak = {
    filter: 'br',

    replacement: function (content, node, options) {
      return options.br + '\n'
    }
  };

  rules.heading = {
    filter: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'],

    replacement: function (content, node, options) {
      var hLevel = Number(node.nodeName.charAt(1));

      if (options.headingStyle === 'setext' && hLevel < 3) {
        var underline = repeat((hLevel === 1 ? '=' : '-'), content.length);
        return (
          '\n\n' + content + '\n' + underline + '\n\n'
        )
      } else {
        return '\n\n' + repeat('#', hLevel) + ' ' + content + '\n\n'
      }
    }
  };

  rules.blockquote = {
    filter: 'blockquote',

    replacement: function (content) {
      content = content.replace(/^\n+|\n+$/g, '');
      content = content.replace(/^/gm, '> ');
      return '\n\n' + content + '\n\n'
    }
  };

  rules.list = {
    filter: ['ul', 'ol'],

    replacement: function (content, node) {
      var parent = node.parentNode;
      if (parent.nodeName === 'LI' && parent.lastElementChild === node) {
        return '\n' + content
      } else {
        return '\n\n' + content + '\n\n'
      }
    }
  };

  rules.listItem = {
    filter: 'li',

    replacement: function (content, node, options) {
      content = content
        .replace(/^\n+/, '') // remove leading newlines
        .replace(/\n+$/, '\n') // replace trailing newlines with just a single one
        .replace(/\n/gm, '\n    '); // indent
      var prefix = options.bulletListMarker + '   ';
      var parent = node.parentNode;
      if (parent.nodeName === 'OL') {
        var start = parent.getAttribute('start');
        var index = Array.prototype.indexOf.call(parent.children, node);
        prefix = (start ? Number(start) + index : index + 1) + '.  ';
      }
      return (
        prefix + content + (node.nextSibling && !/\n$/.test(content) ? '\n' : '')
      )
    }
  };

  rules.indentedCodeBlock = {
    filter: function (node, options) {
      return (
        options.codeBlockStyle === 'indented' &&
        node.nodeName === 'PRE' &&
        node.firstChild &&
        node.firstChild.nodeName === 'CODE'
      )
    },

    replacement: function (content, node, options) {
      return (
        '\n\n    ' +
        node.firstChild.textContent.replace(/\n/g, '\n    ') +
        '\n\n'
      )
    }
  };

  rules.fencedCodeBlock = {
    filter: function (node, options) {
      return (
        options.codeBlockStyle === 'fenced' &&
        node.nodeName === 'PRE' &&
        node.firstChild &&
        node.firstChild.nodeName === 'CODE'
      )
    },

    replacement: function (content, node, options) {
      var className = node.firstChild.className || '';
      var language = (className.match(/language-(\S+)/) || [null, ''])[1];
      var code = node.firstChild.textContent;

      var fenceChar = options.fence.charAt(0);
      var fenceSize = 3;
      var fenceInCodeRegex = new RegExp('^' + fenceChar + '{3,}', 'gm');

      var match;
      while ((match = fenceInCodeRegex.exec(code))) {
        if (match[0].length >= fenceSize) {
          fenceSize = match[0].length + 1;
        }
      }

      var fence = repeat(fenceChar, fenceSize);

      return (
        '\n\n' + fence + language + '\n' +
        code.replace(/\n$/, '') +
        '\n' + fence + '\n\n'
      )
    }
  };

  rules.horizontalRule = {
    filter: 'hr',

    replacement: function (content, node, options) {
      return '\n\n' + options.hr + '\n\n'
    }
  };

  rules.inlineLink = {
    filter: function (node, options) {
      return (
        options.linkStyle === 'inlined' &&
        node.nodeName === 'A' &&
        node.getAttribute('href')
      )
    },

    replacement: function (content, node) {
      var href = node.getAttribute('href');
      var title = node.title ? ' "' + node.title + '"' : '';
      return '[' + content + '](' + href + title + ')'
    }
  };

  rules.referenceLink = {
    filter: function (node, options) {
      return (
        options.linkStyle === 'referenced' &&
        node.nodeName === 'A' &&
        node.getAttribute('href')
      )
    },

    replacement: function (content, node, options) {
      var href = node.getAttribute('href');
      var title = node.title ? ' "' + node.title + '"' : '';
      var replacement;
      var reference;

      switch (options.linkReferenceStyle) {
        case 'collapsed':
          replacement = '[' + content + '][]';
          reference = '[' + content + ']: ' + href + title;
          break
        case 'shortcut':
          replacement = '[' + content + ']';
          reference = '[' + content + ']: ' + href + title;
          break
        default:
          var id = this.references.length + 1;
          replacement = '[' + content + '][' + id + ']';
          reference = '[' + id + ']: ' + href + title;
      }

      this.references.push(reference);
      return replacement
    },

    references: [],

    append: function (options) {
      var references = '';
      if (this.references.length) {
        references = '\n\n' + this.references.join('\n') + '\n\n';
        this.references = []; // Reset references
      }
      return references
    }
  };

  rules.emphasis = {
    filter: ['em', 'i'],

    replacement: function (content, node, options) {
      if (!content.trim()) return ''
      return options.emDelimiter + content + options.emDelimiter
    }
  };

  rules.strong = {
    filter: ['strong', 'b'],

    replacement: function (content, node, options) {
      if (!content.trim()) return ''
      return options.strongDelimiter + content + options.strongDelimiter
    }
  };

  rules.code = {
    filter: function (node) {
      var hasSiblings = node.previousSibling || node.nextSibling;
      var isCodeBlock = node.parentNode.nodeName === 'PRE' && !hasSiblings;

      return node.nodeName === 'CODE' && !isCodeBlock
    },

    replacement: function (content) {
      if (!content.trim()) return ''

      var delimiter = '`';
      var leadingSpace = '';
      var trailingSpace = '';
      var matches = content.match(/`+/gm);
      if (matches) {
        if (/^`/.test(content)) leadingSpace = ' ';
        if (/`$/.test(content)) trailingSpace = ' ';
        while (matches.indexOf(delimiter) !== -1) delimiter = delimiter + '`';
      }

      return delimiter + leadingSpace + content + trailingSpace + delimiter
    }
  };

  rules.image = {
    filter: 'img',

    replacement: function (content, node) {
      var alt = node.alt || '';
      var src = node.getAttribute('src') || '';
      var title = node.title || '';
      var titlePart = title ? ' "' + title + '"' : '';
      return src ? '![' + alt + ']' + '(' + src + titlePart + ')' : ''
    }
  };

  /**
   * Manages a collection of rules used to convert HTML to Markdown
   */

  function Rules (options) {
    this.options = options;
    this._keep = [];
    this._remove = [];

    this.blankRule = {
      replacement: options.blankReplacement
    };

    this.keepReplacement = options.keepReplacement;

    this.defaultRule = {
      replacement: options.defaultReplacement
    };

    this.array = [];
    for (var key in options.rules) this.array.push(options.rules[key]);
  }

  Rules.prototype = {
    add: function (key, rule) {
      this.array.unshift(rule);
    },

    keep: function (filter) {
      this._keep.unshift({
        filter: filter,
        replacement: this.keepReplacement
      });
    },

    remove: function (filter) {
      this._remove.unshift({
        filter: filter,
        replacement: function () {
          return ''
        }
      });
    },

    forNode: function (node) {
      if (node.isBlank) return this.blankRule
      var rule;

      if ((rule = findRule(this.array, node, this.options))) return rule
      if ((rule = findRule(this._keep, node, this.options))) return rule
      if ((rule = findRule(this._remove, node, this.options))) return rule

      return this.defaultRule
    },

    forEach: function (fn) {
      for (var i = 0; i < this.array.length; i++) fn(this.array[i], i);
    }
  };

  function findRule (rules, node, options) {
    for (var i = 0; i < rules.length; i++) {
      var rule = rules[i];
      if (filterValue(rule, node, options)) return rule
    }
    return void 0
  }

  function filterValue (rule, node, options) {
    var filter = rule.filter;
    if (typeof filter === 'string') {
      if (filter === node.nodeName.toLowerCase()) return true
    } else if (Array.isArray(filter)) {
      if (filter.indexOf(node.nodeName.toLowerCase()) > -1) return true
    } else if (typeof filter === 'function') {
      if (filter.call(rule, node, options)) return true
    } else {
      throw new TypeError('`filter` needs to be a string, array, or function')
    }
  }

  /**
   * The collapseWhitespace function is adapted from collapse-whitespace
   * by Luc Thevenard.
   *
   * The MIT License (MIT)
   *
   * Copyright (c) 2014 Luc Thevenard <lucthevenard@gmail.com>
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */

  /**
   * collapseWhitespace(options) removes extraneous whitespace from an the given element.
   *
   * @param {Object} options
   */
  function collapseWhitespace (options) {
    var element = options.element;
    var isBlock = options.isBlock;
    var isVoid = options.isVoid;
    var isPre = options.isPre || function (node) {
      return node.nodeName === 'PRE'
    };

    if (!element.firstChild || isPre(element)) return

    var prevText = null;
    var prevVoid = false;

    var prev = null;
    var node = next(prev, element, isPre);

    while (node !== element) {
      if (node.nodeType === 3 || node.nodeType === 4) { // Node.TEXT_NODE or Node.CDATA_SECTION_NODE
        var text = node.data.replace(/[ \r\n\t]+/g, ' ');

        if ((!prevText || / $/.test(prevText.data)) &&
            !prevVoid && text[0] === ' ') {
          text = text.substr(1);
        }

        // `text` might be empty at this point.
        if (!text) {
          node = remove(node);
          continue
        }

        node.data = text;

        prevText = node;
      } else if (node.nodeType === 1) { // Node.ELEMENT_NODE
        if (isBlock(node) || node.nodeName === 'BR') {
          if (prevText) {
            prevText.data = prevText.data.replace(/ $/, '');
          }

          prevText = null;
          prevVoid = false;
        } else if (isVoid(node)) {
          // Avoid trimming space around non-block, non-BR void elements.
          prevText = null;
          prevVoid = true;
        }
      } else {
        node = remove(node);
        continue
      }

      var nextNode = next(prev, node, isPre);
      prev = node;
      node = nextNode;
    }

    if (prevText) {
      prevText.data = prevText.data.replace(/ $/, '');
      if (!prevText.data) {
        remove(prevText);
      }
    }
  }

  /**
   * remove(node) removes the given node from the DOM and returns the
   * next node in the sequence.
   *
   * @param {Node} node
   * @return {Node} node
   */
  function remove (node) {
    var next = node.nextSibling || node.parentNode;

    node.parentNode.removeChild(node);

    return next
  }

  /**
   * next(prev, current, isPre) returns the next node in the sequence, given the
   * current and previous nodes.
   *
   * @param {Node} prev
   * @param {Node} current
   * @param {Function} isPre
   * @return {Node}
   */
  function next (prev, current, isPre) {
    if ((prev && prev.parentNode === current) || isPre(current)) {
      return current.nextSibling || current.parentNode
    }

    return current.firstChild || current.nextSibling || current.parentNode
  }

  /*
   * Set up window for Node.js
   */

  var root = (typeof window !== 'undefined' ? window : {});

  /*
   * Parsing HTML strings
   */

  function canParseHTMLNatively () {
    var Parser = root.DOMParser;
    var canParse = false;

    // Adapted from https://gist.github.com/1129031
    // Firefox/Opera/IE throw errors on unsupported types
    try {
      // WebKit returns null on unsupported types
      if (new Parser().parseFromString('', 'text/html')) {
        canParse = true;
      }
    } catch (e) {}

    return canParse
  }

  function createHTMLParser () {
    var Parser = function () {};

    {
      if (shouldUseActiveX()) {
        Parser.prototype.parseFromString = function (string) {
          var doc = new window.ActiveXObject('htmlfile');
          doc.designMode = 'on'; // disable on-page scripts
          doc.open();
          doc.write(string);
          doc.close();
          return doc
        };
      } else {
        Parser.prototype.parseFromString = function (string) {
          var doc = document.implementation.createHTMLDocument('');
          doc.open();
          doc.write(string);
          doc.close();
          return doc
        };
      }
    }
    return Parser
  }

  function shouldUseActiveX () {
    var useActiveX = false;
    try {
      document.implementation.createHTMLDocument('').open();
    } catch (e) {
      if (window.ActiveXObject) useActiveX = true;
    }
    return useActiveX
  }

  var HTMLParser = canParseHTMLNatively() ? root.DOMParser : createHTMLParser();

  function RootNode (input) {
    var root;
    if (typeof input === 'string') {
      var doc = htmlParser().parseFromString(
        // DOM parsers arrange elements in the <head> and <body>.
        // Wrapping in a custom element ensures elements are reliably arranged in
        // a single element.
        '<x-turndown id="turndown-root">' + input + '</x-turndown>',
        'text/html'
      );
      root = doc.getElementById('turndown-root');
    } else {
      root = input.cloneNode(true);
    }
    collapseWhitespace({
      element: root,
      isBlock: isBlock,
      isVoid: isVoid
    });

    return root
  }

  var _htmlParser;
  function htmlParser () {
    _htmlParser = _htmlParser || new HTMLParser();
    return _htmlParser
  }

  function Node (node) {
    node.isBlock = isBlock(node);
    node.isCode = node.nodeName.toLowerCase() === 'code' || node.parentNode.isCode;
    node.isBlank = isBlank(node);
    node.flankingWhitespace = flankingWhitespace(node);
    return node
  }

  function isBlank (node) {
    return (
      ['A', 'TH', 'TD', 'IFRAME', 'SCRIPT', 'AUDIO', 'VIDEO'].indexOf(node.nodeName) === -1 &&
      /^\s*$/i.test(node.textContent) &&
      !isVoid(node) &&
      !hasVoid(node)
    )
  }

  function flankingWhitespace (node) {
    var leading = '';
    var trailing = '';

    if (!node.isBlock) {
      var hasLeading = /^\s/.test(node.textContent);
      var hasTrailing = /\s$/.test(node.textContent);
      var blankWithSpaces = node.isBlank && hasLeading && hasTrailing;

      if (hasLeading && !isFlankedByWhitespace('left', node)) {
        leading = ' ';
      }

      if (!blankWithSpaces && hasTrailing && !isFlankedByWhitespace('right', node)) {
        trailing = ' ';
      }
    }

    return { leading: leading, trailing: trailing }
  }

  function isFlankedByWhitespace (side, node) {
    var sibling;
    var regExp;
    var isFlanked;

    if (side === 'left') {
      sibling = node.previousSibling;
      regExp = / $/;
    } else {
      sibling = node.nextSibling;
      regExp = /^ /;
    }

    if (sibling) {
      if (sibling.nodeType === 3) {
        isFlanked = regExp.test(sibling.nodeValue);
      } else if (sibling.nodeType === 1 && !isBlock(sibling)) {
        isFlanked = regExp.test(sibling.textContent);
      }
    }
    return isFlanked
  }

  var reduce = Array.prototype.reduce;
  var leadingNewLinesRegExp = /^\n*/;
  var trailingNewLinesRegExp = /\n*$/;
  var escapes = [
    [/\\/g, '\\\\'],
    [/\*/g, '\\*'],
    [/^-/g, '\\-'],
    [/^\+ /g, '\\+ '],
    [/^(=+)/g, '\\$1'],
    [/^(#{1,6}) /g, '\\$1 '],
    [/`/g, '\\`'],
    [/^~~~/g, '\\~~~'],
    [/\[/g, '\\['],
    [/\]/g, '\\]'],
    [/^>/g, '\\>'],
    [/_/g, '\\_'],
    [/^(\d+)\. /g, '$1\\. ']
  ];

  function TurndownService (options) {
    if (!(this instanceof TurndownService)) return new TurndownService(options)

    var defaults = {
      rules: rules,
      headingStyle: 'setext',
      hr: '* * *',
      bulletListMarker: '*',
      codeBlockStyle: 'indented',
      fence: '```',
      emDelimiter: '_',
      strongDelimiter: '**',
      linkStyle: 'inlined',
      linkReferenceStyle: 'full',
      br: '  ',
      blankReplacement: function (content, node) {
        return node.isBlock ? '\n\n' : ''
      },
      keepReplacement: function (content, node) {
        return node.isBlock ? '\n\n' + node.outerHTML + '\n\n' : node.outerHTML
      },
      defaultReplacement: function (content, node) {
        return node.isBlock ? '\n\n' + content + '\n\n' : content
      }
    };
    this.options = extend({}, defaults, options);
    this.rules = new Rules(this.options);
  }

  TurndownService.prototype = {
    /**
     * The entry point for converting a string or DOM node to Markdown
     * @public
     * @param {String|HTMLElement} input The string or DOM node to convert
     * @returns A Markdown representation of the input
     * @type String
     */

    turndown: function (input) {
      if (!canConvert(input)) {
        throw new TypeError(
          input + ' is not a string, or an element/document/fragment node.'
        )
      }

      if (input === '') return ''

      var output = process.call(this, new RootNode(input));
      return postProcess.call(this, output)
    },

    /**
     * Add one or more plugins
     * @public
     * @param {Function|Array} plugin The plugin or array of plugins to add
     * @returns The Turndown instance for chaining
     * @type Object
     */

    use: function (plugin) {
      if (Array.isArray(plugin)) {
        for (var i = 0; i < plugin.length; i++) this.use(plugin[i]);
      } else if (typeof plugin === 'function') {
        plugin(this);
      } else {
        throw new TypeError('plugin must be a Function or an Array of Functions')
      }
      return this
    },

    /**
     * Adds a rule
     * @public
     * @param {String} key The unique key of the rule
     * @param {Object} rule The rule
     * @returns The Turndown instance for chaining
     * @type Object
     */

    addRule: function (key, rule) {
      this.rules.add(key, rule);
      return this
    },

    /**
     * Keep a node (as HTML) that matches the filter
     * @public
     * @param {String|Array|Function} filter The unique key of the rule
     * @returns The Turndown instance for chaining
     * @type Object
     */

    keep: function (filter) {
      this.rules.keep(filter);
      return this
    },

    /**
     * Remove a node that matches the filter
     * @public
     * @param {String|Array|Function} filter The unique key of the rule
     * @returns The Turndown instance for chaining
     * @type Object
     */

    remove: function (filter) {
      this.rules.remove(filter);
      return this
    },

    /**
     * Escapes Markdown syntax
     * @public
     * @param {String} string The string to escape
     * @returns A string with Markdown syntax escaped
     * @type String
     */

    escape: function (string) {
      return escapes.reduce(function (accumulator, escape) {
        return accumulator.replace(escape[0], escape[1])
      }, string)
    }
  };

  /**
   * Reduces a DOM node down to its Markdown string equivalent
   * @private
   * @param {HTMLElement} parentNode The node to convert
   * @returns A Markdown representation of the node
   * @type String
   */

  function process (parentNode) {
    var self = this;
    return reduce.call(parentNode.childNodes, function (output, node) {
      node = new Node(node);

      var replacement = '';
      if (node.nodeType === 3) {
        replacement = node.isCode ? node.nodeValue : self.escape(node.nodeValue);
      } else if (node.nodeType === 1) {
        replacement = replacementForNode.call(self, node);
      }

      return join(output, replacement)
    }, '')
  }

  /**
   * Appends strings as each rule requires and trims the output
   * @private
   * @param {String} output The conversion output
   * @returns A trimmed version of the ouput
   * @type String
   */

  function postProcess (output) {
    var self = this;
    this.rules.forEach(function (rule) {
      if (typeof rule.append === 'function') {
        output = join(output, rule.append(self.options));
      }
    });

    return output.replace(/^[\t\r\n]+/, '').replace(/[\t\r\n\s]+$/, '')
  }

  /**
   * Converts an element node to its Markdown equivalent
   * @private
   * @param {HTMLElement} node The node to convert
   * @returns A Markdown representation of the node
   * @type String
   */

  function replacementForNode (node) {
    var rule = this.rules.forNode(node);
    var content = process.call(this, node);
    var whitespace = node.flankingWhitespace;
    if (whitespace.leading || whitespace.trailing) content = content.trim();
    return (
      whitespace.leading +
      rule.replacement(content, node, this.options) +
      whitespace.trailing
    )
  }

  /**
   * Determines the new lines between the current output and the replacement
   * @private
   * @param {String} output The current conversion output
   * @param {String} replacement The string to append to the output
   * @returns The whitespace to separate the current output and the replacement
   * @type String
   */

  function separatingNewlines (output, replacement) {
    var newlines = [
      output.match(trailingNewLinesRegExp)[0],
      replacement.match(leadingNewLinesRegExp)[0]
    ].sort();
    var maxNewlines = newlines[newlines.length - 1];
    return maxNewlines.length < 2 ? maxNewlines : '\n\n'
  }

  function join (string1, string2) {
    var separator = separatingNewlines(string1, string2);

    // Remove trailing/leading newlines and replace with separator
    string1 = string1.replace(trailingNewLinesRegExp, '');
    string2 = string2.replace(leadingNewLinesRegExp, '');

    return string1 + separator + string2
  }

  /**
   * Determines whether an input can be converted
   * @private
   * @param {String|HTMLElement} input Describe this parameter
   * @returns Describe what it returns
   * @type String|Object|Array|Boolean|Number
   */

  function canConvert (input) {
    return (
      input != null && (
        typeof input === 'string' ||
        (input.nodeType && (
          input.nodeType === 1 || input.nodeType === 9 || input.nodeType === 11
        ))
      )
    )
  }

  return TurndownService;

}());