hast-util-to-estree

hast utility to transform to estree (JSX).

What is this?
When should I use this?
Install
Use
API
Types
Compatibility
Security
Related
Contribute
License

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 14.14+ and 16.0+), install with npm:

npm install hast-util-to-estree

In Deno with esm.sh:

import {toEstree} from 'https://esm.sh/hast-util-to-estree@2'

In browsers with esm.sh:

<script type="module">
  import {toEstree} from 'https://esm.sh/hast-util-to-estree@2?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 {fromHtml} from 'hast-util-from-html'
import {toEstree} from 'hast-util-to-estree'
import {toJs, jsx} from 'estree-util-to-js'

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 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.

Parameters

tree (HastNode) — hast tree
options (Options, optional) — configuration

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.

`Handle`

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

Parameters

node (HastNode) — expected hast node
state (State) — info passed around about the current state

Returns

JSX child (JsxChild, optional).

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

`Options`

Configuration (TypeScript type).

Fields

`space`

Which space the document is in (Space, default: 'html').

When an <svg> element is found in the HTML space, this package already automatically switches to and from the SVG space when entering and exiting it.

`handlers`

Object mapping node types to functions handling the corresponding nodes (Record<string, Handle>, optional).

Merged into the defaults. See Handle.

`Space`

Namespace (TypeScript type).

Type

type Space = 'html' | 'svg'

`State`

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

Fields

schema (Schema) — current schema
comments (Array<EstreeComment>) — list of estree comments
esm (Array<EstreeNode>) — list of top-level estree nodes
handle ((node: HastNode) => EstreeJsxChild | void) — transform a hast node to estree
handle ((node: HastParent) => EstreeJsxChild | void) — transform children of a hast parent to estree
patch ((from: HastNode, to: EstreeNode) => void) — take positional info from from (use inherit if you also want data)
inherit ((from: HastNode, to: EstreeNode) => void) — take positional info and data from from (use patch if you don’t want data)
createJsxAttributeName ((name: string) => EstreeJsxAttributeName) — create a JSX attribute name
createJsxElementName ((name: string) => EstreeJsxElementName) — create a JSX attribute name

Types

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

Compatibility

Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 14.14+ and 16.0+. Our projects sometimes work with older versions, but this is not guaranteed.

Security

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

hastscript — hyperscript compatible interface for creating nodes
hast-util-from-dom — transform a DOM tree to hast
estree-util-build-jsx — transform JSX to function calls

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.