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hast-util-to-estree

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hast utility to transform to estree (JSX).

Contents

What is this?

This package is a utility that takes a hast (HTML) syntax tree as input and turns it into an estree (JavaScript) syntax tree (with a JSX extension). This package also supports embedded MDX nodes.

When should I use this?

This project is useful when you want to embed HTML as JSX inside JS while working with syntax trees. This is used in MDX.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install hast-util-to-estree

In Deno with esm.sh:

import {toEstree} from 'https://esm.sh/hast-util-to-estree@3'

In browsers with esm.sh:

<script type="module">
  import {toEstree} from 'https://esm.sh/hast-util-to-estree@3?bundle'
</script>

Use

Say our module example.html contains:

<!doctype html>
<html lang=en>
<title>Hi!</title>
<link rel=stylesheet href=index.css>
<h1>Hello, world!</h1>
<a download style="width:1;height:10px"></a>
<!--commentz-->
<svg xmlns="http://www.w3.org/2000/svg">
  <title>SVG `&lt;ellipse&gt;` element</title>
  <ellipse
    cx="120"
    cy="70"
    rx="100"
    ry="50"
  />
</svg>
<script src="index.js"></script>

…and our module example.js looks as follows:

import fs from 'node:fs/promises'
import {jsx, toJs} from 'estree-util-to-js'
import {fromHtml} from 'hast-util-from-html'
import {toEstree} from 'hast-util-to-estree'

const hast = fromHtml(await fs.readFile('example.html'))

const estree = toEstree(hast)

console.log(toJs(estree, {handlers: jsx}).value)

…now running node example.js (and prettier) yields:

/* Commentz */
;<>
  <html lang="en">
    <head>
      <title>{'Hi!'}</title>
      {'\n'}
      <link rel="stylesheet" href="index.css" />
      {'\n'}
    </head>
    <body>
      <h1>{'Hello, world!'}</h1>
      {'\n'}
      <a
        download
        style={{
          width: '1',
          height: '10px'
        }}
      />
      {'\n'}
      {}
      {'\n'}
      <svg xmlns="http://www.w3.org/2000/svg">
        {'\n  '}
        <title>{'SVG `<ellipse>` element'}</title>
        {'\n  '}
        <ellipse cx="120" cy="70" rx="100" ry="50" />
        {'\n'}
      </svg>
      {'\n'}
      <script src="index.js" />
      {'\n'}
    </body>
  </html>
</>

API

This package exports the identifiers defaultHandlers and toEstree. There is no default export.

toEstree(tree[, options])

Transform a hast tree (with embedded MDX nodes) into an estree (with JSX nodes).

Notes
Comments

Comments are attached to the tree in their neighbouring nodes (recast, babel style) and also added as a comments array on the program node (espree style). You may have to do program.comments = undefined for certain compilers.

Frameworks

There are differences between what JSX frameworks accept, such as whether they accept class or className, or background-color or backgroundColor.

For JSX components written in MDX, the author has to be aware of this difference and write code accordingly. For hast elements transformed by this project, this will be handled through options.

FrameworkelementAttributeNameCasestylePropertyNameCase
Preact'html''dom'
React'react''dom'
Solid'html''css'
Vue'html''dom'
Parameters
Returns

estree program node (Program).

The program’s last child in body is most likely an ExpressionStatement, whose expression is a JSXFragment or a JSXElement.

Typically, there is only one node in body, however, this utility also supports embedded MDX nodes in the HTML (when mdast-util-mdx is used with mdast to parse markdown before passing its nodes through to hast). When MDX ESM import/exports are used, those nodes are added before the fragment or element in body.

There aren’t many great estree serializers out there that support JSX. To do that, you can use estree-util-to-js. Or, use estree-util-build-jsx to turn JSX into function calls, and then serialize with whatever (astring, escodegen).

defaultHandlers

Default handlers for elements (Record<string, Handle>).

Each key is a node type, each value is a Handle.

ElementAttributeNameCase

Specify casing to use for attribute names (TypeScript type).

HTML casing is for example class, stroke-linecap, xml:lang. React casing is for example className, strokeLinecap, xmlLang.

Type
type ElementAttributeNameCase = 'html' | 'react'

Handle

Turn a hast node into an estree node (TypeScript type).

Parameters
Returns

JSX child (JsxChild, optional).

You can also add more results to state.esm and state.comments.

Options

Configuration (TypeScript type).

Fields

Space

Namespace (TypeScript type).

Type
type Space = 'html' | 'svg'

State

Info passed around about the current state (TypeScript type).

Fields

StylePropertyNameCase

Casing to use for property names in style objects (TypeScript type).

CSS casing is for example background-color and -webkit-line-clamp. DOM casing is for example backgroundColor and WebkitLineClamp.

Type
type StylePropertyNameCase = 'css' | 'dom'

Types

This package is fully typed with TypeScript. It exports the additional types ElementAttributeNameCase, Handle, Options, Space, State, and StylePropertyNameCase.

Compatibility

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, hast-util-to-estree@^3, compatible with Node.js 16.

Security

You’re working with JavaScript. It’s not safe.

Related

Contribute

See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Titus Wormer

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