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SAX-style (Simple API for XML) in TypeScript
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sax-ts 📦

Simple API for XML in TypeScript

Build Status Coverage Status License NPM DenoLib

A SAX-style parser for XML and HTML.

Designed with deno in mind, so it's browser compatible

What This Is

  • A very simple tool to parse through an XML string.
  • A handy way to deal with RSS and other mostly-ok-but-kinda-broken XML docs.
  • A perfect way to parse 80 GB of XML data and don't burn your laptop :)



import { SAXParser } from '';
// for semver, use "@%5E1.2.8", which is the urlencoded version of "@^1.2.8"
const strict: boolean = true; // change to false for HTML parsing
const options: {} = {}; // refer to "Arguments" section
const parser = new SAXParser(strict, options);

parser.onerror = function (e) {
  // an error happened.
parser.ontext = function (t) {
  // got some text.  t is the string of text.
  console.log('onText: ', t)
parser.onopentag = function (node) {
  // opened a tag.  node has "name" and "attributes"
  console.log('onOpenTag: ', node)
parser.onattribute = function (attr) {
  // an attribute.  attr has "name" and "value"
  console.log('onAttribute: ', attr)
parser.onend = function () {
  // parser stream is done, and ready to have more stuff written to it.
  console.warn('end of XML')

parser.write('<xml>Hello, <who name="world">world</who>!</xml>').close();


Pass the following arguments to the parser function. All are optional.

strict - Boolean. Disabled "forgiving" mode. Default: false.

options - Object bag of settings regarding string formatting. All default to false.

Settings supported:

  • trim - Boolean. Whether or not to trim text and comment nodes.
  • normalize - Boolean. If true, then turn any whitespace into a single space.
  • lowercase - Boolean. If true, then lowercase tag names and attribute names in loose mode, rather than uppercasing them.
  • xmlns - Boolean. If true, then namespaces are supported.
  • position - Boolean. If false, then don't track line/col/position.
  • strictEntities - Boolean. If true, only parse predefined XML entities (&amp;, &apos;, &gt;, &lt;, and &quot;)


write - Write bytes onto the stream. You don't have to do this all at once. You can keep writing as much as you want.

close - Close the stream. Once closed, no more data may be written until it is done processing the buffer, which is signaled by the end event.

resume - To gracefully handle errors, assign a listener to the error event. Then, when the error is taken care of, you can call resume to continue parsing. Otherwise, the parser will not continue while in an error state.


All events emit with a single argument. To listen to an event, assign a function to on<eventname>. Functions get executed in the this-context of the parser object. The list of supported events are also in the exported EVENTS array.

error - Indication that something bad happened. The error will be hanging out on parser.error, and must be deleted before parsing can continue. By listening to this event, you can keep an eye on that kind of stuff. Note: this happens much more in strict mode. Argument: instance of Error.

//TODO: currently `error` is protected, need to expose it to user somehow.

text - Text node. Argument: string of text.

doctype - The <!DOCTYPE declaration. Argument: doctype string.

processinginstruction - Stuff like <?xml foo="blerg" ?>. Argument: object with name and body members. Attributes are not parsed, as processing instructions have implementation dependent semantics.

sgmldeclaration - Random SGML declarations. Stuff like <!ENTITY p> would trigger this kind of event. This is a weird thing to support, so it might go away at some point. SAX isn't intended to be used to parse SGML, after all.

opentagstart - Emitted immediately when the tag name is available, but before any attributes are encountered. Argument: object with a name field and an empty attributes set. Note that this is the same object that will later be emitted in the opentag event.

opentag - An opening tag. Argument: object with name and attributes. In non-strict mode, tag names are uppercased, unless the lowercase option is set. If the xmlns option is set, then it will contain namespace binding information on the ns member, and will have a local, prefix, and uri member.

closetag - A closing tag. In loose mode, tags are auto-closed if their parent closes. In strict mode, well-formedness is enforced. Note that self-closing tags will have closeTag emitted immediately after openTag. Argument: tag name.

attribute - An attribute node. Argument: object with name and value. In non-strict mode, attribute names are in upper-case, unless the lowercase option is set. If the xmlns option is set, it will also contains namespace information.

comment - A comment node. Argument: the string of the comment.

opencdata - The opening tag of a <![CDATA[ block.

cdata - The text of a <![CDATA[ block. Since <![CDATA[ blocks can get quite large, this event may fire multiple times for a single block, if it is broken up into multiple write()s. Argument: the string of random character data.

closecdata - The closing tag (]]>) of a <![CDATA[ block.

opennamespace - If the xmlns option is set, then this event will signal the start of a new namespace binding.

closenamespace - If the xmlns option is set, then this event will signal the end of a namespace binding.

end - Indication that the closed stream has ended.

ready - Indication that the stream has reset, and is ready to be written to.

noscript - In non-strict mode, <script> tags trigger a "script" event, and their contents are not checked for special xml characters. If you pass noscript: true, then this behavior is suppressed.


What This Is (probably) Not

  • An HTML Parser - That's a fine goal, but this isn't it. It's just XML.
  • A DOM Builder - You can use it to build an object model out of XML, but it does not do that out of the box.
  • XSLT - No DOM = no querying.
  • 100% Compliant with (some other SAX implementation) - Most SAX implementations are in Java and do a lot more than this does.
  • An XML Validator - It does a little validation when in strict mode, but not much.
  • A Schema-Aware XSD Thing - Schemas are an exercise in fetishistic masochism.
  • A DTD-aware Thing - Fetching DTDs is a much bigger job.

Regarding <!DOCTYPEs and <!ENTITYs

The parser will handle the basic XML entities in text nodes and attribute values: &amp; &lt; &gt; &apos; &quot;. It's possible to define additional entities in XML by putting them in the DTD. This parser does not do anything with that.

Unknown entities will fail in strict mode, and in loose mode, will pass through unmolested.

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