posthtml-parser

What is posthtml-parser?

The posthtml-parser npm package is a tool used to parse HTML into an Abstract Syntax Tree (AST). This allows developers to manipulate HTML content programmatically, making it easier to perform tasks such as transforming HTML structures, extracting specific elements, and integrating with other tools in the PostHTML ecosystem.

What are posthtml-parser's main functionalities?

Parsing HTML to AST

This feature allows you to parse a string of HTML into an Abstract Syntax Tree (AST). The AST can then be manipulated programmatically.

const parse = require('posthtml-parser');
const html = '<div class="example">Hello World</div>';
const ast = parse(html);
console.log(ast);

Handling HTML fragments

This feature allows you to parse HTML fragments and control parsing options such as whether to convert tag names to lowercase.

const parse = require('posthtml-parser');
const fragment = '<span>Fragment</span>';
const ast = parse(fragment, { lowerCaseTags: false });
console.log(ast);

Integration with PostHTML plugins

This feature demonstrates how to integrate the parser with PostHTML plugins to transform HTML content. In this example, a plugin is used to change all <div> tags to <section> tags.

const posthtml = require('posthtml');
const parse = require('posthtml-parser');
const html = '<div class="example">Hello World</div>';
posthtml()
  .use(tree => {
    tree.match({ tag: 'div' }, node => {
      node.tag = 'section';
      return node;
    });
  })
  .process(html)
  .then(result => console.log(result.html));

Other packages similar to posthtml-parser

htmlparser2

htmlparser2 is a fast and forgiving HTML/XML parser. It is similar to posthtml-parser in that it parses HTML into a tree structure, but it is more focused on speed and flexibility. It also supports streaming and can handle large documents efficiently.

parse5

parse5 is a highly compliant HTML parser that closely follows the WHATWG HTML specification. It is similar to posthtml-parser in its ability to parse HTML into an AST, but it is known for its strict adherence to web standards and comprehensive support for HTML5 features.

cheerio

cheerio is a fast, flexible, and lean implementation of core jQuery designed specifically for the server. It parses HTML and XML into a DOM-like structure, allowing for jQuery-like manipulation of the document. While it offers similar parsing capabilities, it is more focused on providing a familiar API for DOM manipulation.

README

PostHTML Parser

Parse HTML/XML to PostHTML AST

Installation

npm install posthtml-parser

Usage

Input HTML:

<a class="animals" href="#">
  <span class="animals__cat" style="background: url(cat.png)">Cat</span>
</a>

Parse with posthtml-parser:

import fs from 'fs'
import { parser } from 'posthtml-parser'

const html = fs.readFileSync('path/to/input.html', 'utf-8')

console.log(parser(html))

Resulting PostHTML AST:

[
  {
    tag: 'a',
    attrs: {
      class: 'animals',
      href: '#'
    },
    content: [
      '\n    ',
      {
        tag: 'span',
        attrs: {
          class: 'animals__cat',
          style: 'background: url(cat.png)'
        },
        content: ['Cat']
      },
      '\n'
    ]
  }
]

PostHTML AST Format

Any parser used with PostHTML should return a standard PostHTML Abstract Syntax Tree (AST).

Fortunately, this is a very easy format to produce and understand. The AST is an array that can contain strings and objects. Strings represent plain text content, while objects represent HTML tags.

Tag objects generally look like this:

{
  tag: 'div',
  attrs: {
    class: 'foo'
  },
  content: ['hello world!']
}

Tag objects can contain three keys:

• The tag key takes the name of the tag as the value. This can include custom tags.
• The optional attrs key takes an object with key/value pairs representing the attributes of the html tag. A boolean attribute has an empty string as its value.
• The optional content key takes an array as its value, which is a PostHTML AST. In this manner, the AST is a tree that should be walked recursively.

Options

directives

Type: Array
Default: [{name: '!doctype', start: '<', end: '>'}]

Adds processing of custom directives.

The property name in custom directives can be of String or RegExp type.

xmlMode

Type: Boolean
Default: false

Indicates whether special tags (<script> and <style>) should get special treatment and if "empty" tags (eg. <br>) can have children. If false, the content of special tags will be text only.

For feeds and other XML content (documents that don't consist of HTML), set this to true.

decodeEntities

Type: Boolean
Default: false

If set to true, entities within the document will be decoded.

lowerCaseTags

Type: Boolean
Default: false

If set to true, all tags will be lowercased. If xmlMode is disabled.

lowerCaseAttributeNames

Type: Boolean
Default: false

If set to true, all attribute names will be lowercased.

This has noticeable impact on speed.

recognizeCDATA

Type: Boolean
Default: false

If set to true, CDATA sections will be recognized as text even if the xmlMode option is not enabled.

If xmlMode is set to true, then CDATA sections will always be recognized as text.

recognizeSelfClosing

Type: Boolean
Default: false

If set to true, self-closing tags will trigger the onclosetag event even if xmlMode is not set to true.

If xmlMode is set to true, then self-closing tags will always be recognized.

sourceLocations

Type: Boolean
Default: false

If set to true, AST nodes will have a location property containing the start and end line and column position of the node.

recognizeNoValueAttribute

Type: Boolean
Default: false

If set to true, AST nodes will recognize attribute with no value and mark as true which will be correctly rendered by posthtml-render package.