htmlparser2

What is htmlparser2?

The htmlparser2 npm package is a fast and forgiving HTML and XML parser. It can parse HTML or XML into a DOM-like structure, which can then be manipulated or serialized. It is stream-based, which means it can handle large documents in a memory-efficient manner.

What are htmlparser2's main functionalities?

Parsing HTML to DOM

This feature allows you to parse HTML and handle different parts of the document as they are parsed. The example code sets up event handlers for opening tags, text content, and closing tags, and then parses a simple HTML string.

const htmlparser2 = require('htmlparser2');
const parser = new htmlparser2.Parser({
  onopentag(name, attributes) {
    console.log(name, attributes);
  },
  ontext(text) {
    console.log(text);
  },
  onclosetag(tagname) {
    console.log(tagname);
  }
}, { decodeEntities: true });
parser.write('<div class="test">Hello World</div>');
parser.end();

Streaming Interface

This feature allows you to parse HTML from a stream, such as a file or network response. The example code creates a readable stream from a file and pipes it to the htmlparser2 stream, which logs tag openings, text content, and tag closings.

const htmlparser2 = require('htmlparser2');
const fs = require('fs');
const parser = new htmlparser2.WritableStream({
  onopentag(name) {
    console.log('Opened tag:', name);
  },
  ontext(text) {
    console.log('Text:', text);
  },
  onclosetag(name) {
    console.log('Closed tag:', name);
  }
});
fs.createReadStream('example.html').pipe(parser);

DOM Tree Manipulation

This feature allows you to manipulate the DOM tree after parsing. The example code parses an HTML string into a DOM tree, changes the class attribute of the first element, and then serializes the modified element back to an HTML string.

const htmlparser2 = require('htmlparser2');
const dom = htmlparser2.parseDocument('<div class="test">Hello World</div>');
const divElement = dom.children[0];
divElement.attribs.class = 'new-class';
const serialized = htmlparser2.DomUtils.getOuterHTML(divElement);
console.log(serialized);

Other packages similar to htmlparser2

cheerio

Cheerio is a fast, flexible, and lean implementation of core jQuery designed specifically for the server. It uses a parser similar to htmlparser2 but provides a jQuery-like API for manipulating the resulting data structure. It is generally easier to use if you are familiar with jQuery.

jsdom

jsdom is a pure-JavaScript implementation of many web standards, notably the WHATWG DOM and HTML Standards, for use with Node.js. It is heavier than htmlparser2 but provides a more complete simulation of a web browser's environment, including the ability to execute scripts in the context of the parsed document.

parse5

parse5 is an HTML parsing/serialization toolset for Node.js that adheres to the HTML5 specification. It is more standards-compliant than htmlparser2 but may be slower due to its focus on correctness over speed.

README

htmlparser2

The fast & forgiving HTML/XML parser.

htmlparser2 is the fastest HTML parser, and takes some shortcuts to get there. If you need strict HTML spec compliance, have a look at parse5.

Installation

npm install htmlparser2

A live demo of htmlparser2 is available on AST Explorer.

Ecosystem

Name	Description
htmlparser2	Fast & forgiving HTML/XML parser
domhandler	Handler for htmlparser2 that turns documents into a DOM
domutils	Utilities for working with domhandler's DOM
css-select	CSS selector engine, compatible with domhandler's DOM
cheerio	The jQuery API for domhandler's DOM
dom-serializer	Serializer for domhandler's DOM

Usage

htmlparser2 itself provides a callback interface that allows consumption of documents with minimal allocations. For a more ergonomic experience, read Getting a DOM below.

import * as htmlparser2 from "htmlparser2";

const parser = new htmlparser2.Parser({
    onopentag(name, attributes) {
        /*
         * This fires when a new tag is opened.
         *
         * If you don't need an aggregated `attributes` object,
         * have a look at the `onopentagname` and `onattribute` events.
         */
        if (name === "script" && attributes.type === "text/javascript") {
            console.log("JS! Hooray!");
        }
    },
    ontext(text) {
        /*
         * Fires whenever a section of text was processed.
         *
         * Note that this can fire at any point within text and you might
         * have to stitch together multiple pieces.
         */
        console.log("-->", text);
    },
    onclosetag(tagname) {
        /*
         * Fires when a tag is closed.
         *
         * You can rely on this event only firing when you have received an
         * equivalent opening tag before. Closing tags without corresponding
         * opening tags will be ignored.
         */
        if (tagname === "script") {
            console.log("That's it?!");
        }
    },
});
parser.write(
    "Xyz <script type='text/javascript'>const foo = '<<bar>>';</script>",
);
parser.end();

Output (with multiple text events combined):

--> Xyz
JS! Hooray!
--> const foo = '<<bar>>';
That's it?!

This example only shows three of the possible events. Read more about the parser, its events and options in the wiki.

Usage with streams

While the Parser interface closely resembles Node.js streams, it's not a 100% match. Use the WritableStream interface to process a streaming input:

import { WritableStream } from "htmlparser2/lib/WritableStream";

const parserStream = new WritableStream({
    ontext(text) {
        console.log("Streaming:", text);
    },
});

const htmlStream = fs.createReadStream("./my-file.html");
htmlStream.pipe(parserStream).on("finish", () => console.log("done"));

Getting a DOM

The DomHandler produces a DOM (document object model) that can be manipulated using the DomUtils helper.

import * as htmlparser2 from "htmlparser2";

const dom = htmlparser2.parseDocument(htmlString);

The DomHandler, while still bundled with this module, was moved to its own module. Have a look at that for further information.

Parsing Feeds

htmlparser2 makes it easy to parse RSS, RDF and Atom feeds, by providing a parseFeed method:

const feed = htmlparser2.parseFeed(content, options);

Performance

After having some artificial benchmarks for some time, @AndreasMadsen published his htmlparser-benchmark, which benchmarks HTML parses based on real-world websites.

At the time of writing, the latest versions of all supported parsers show the following performance characteristics on GitHub Actions (sourced from here):

htmlparser2        : 2.17215 ms/file ± 3.81587
node-html-parser   : 2.35983 ms/file ± 1.54487
html5parser        : 2.43468 ms/file ± 2.81501
neutron-html5parser: 2.61356 ms/file ± 1.70324
htmlparser2-dom    : 3.09034 ms/file ± 4.77033
html-dom-parser    : 3.56804 ms/file ± 5.15621
libxmljs           : 4.07490 ms/file ± 2.99869
htmljs-parser      : 6.15812 ms/file ± 7.52497
parse5             : 9.70406 ms/file ± 6.74872
htmlparser         : 15.0596 ms/file ± 89.0826
html-parser        : 28.6282 ms/file ± 22.6652
saxes              : 45.7921 ms/file ± 128.691
html5              : 120.844 ms/file ± 153.944

How does this module differ from node-htmlparser?

In 2011, this module started as a fork of the htmlparser module. htmlparser2 was rewritten multiple times and, while it maintains an API that's mostly compatible with htmlparser, the projects don't share any code anymore.

The parser now provides a callback interface inspired by sax.js (originally targeted at readabilitySAX). As a result, old handlers won't work anymore.

The DefaultHandler was renamed to clarify its purpose (to DomHandler). The old name is still available when requiring htmlparser2 and your code should work as expected.

The RssHandler was replaced with a getFeed function that takes a DomHandler DOM and returns a feed object. There is a parseFeed helper function that can be used to parse a feed from a string.

Security contact information

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