estree utility to turn JSX into function calls: <x /> -> h('x')!

• What is this?
• When should I use this?
• Install
• Use
• API
  • buildJsx(tree, options?)
  • Options
  • Runtime
• Examples
  • Example: use with Acorn
• Types
• Compatibility
• Related
• Security
• Contribute
• License

This package is a utility that takes an estree (JavaScript) syntax tree as input that contains embedded JSX nodes (elements, fragments) and turns them into function calls.

If you already have a tree and only need to compile JSX away, use this. If you have code, use something like SWC or esbuild instead.

This package is ESM only. In Node.js (version 14.14+ and 16.0+), install with npm:

npm install estree-util-build-jsx

In Deno with esm.sh:

import {buildJsx} from 'https://esm.sh/estree-util-build-jsx@2'

In browsers with esm.sh:

<script type="module">
  import {buildJsx} from 'https://esm.sh/estree-util-build-jsx@2?bundle'
</script>

Say we have the following example.jsx:

import x from 'xastscript'

console.log(
  <album id={123}>
    <name>Born in the U.S.A.</name>
    <artist>Bruce Springsteen</artist>
    <releasedate date="1984-04-06">April 6, 1984</releasedate>
  </album>
)

console.log(
  <>
    {1 + 1}
    <self-closing />
    <x name key="value" key={expression} {...spread} />
  </>
)

…and next to it a module example.js:

import fs from 'node:fs/promises'
import {fromJs} from 'esast-util-from-js'
import {buildJsx} from 'estree-util-build-jsx'
import {toJs} from 'estree-util-to-js'
import jsx from 'acorn-jsx'

const doc = String(await fs.readFile('example.jsx'))

const tree = fromJs(doc, {module: true, plugins: [jsx()]})

buildJsx(tree, {pragma: 'x', pragmaFrag: 'null'})

console.log(toJs(tree).value)

…now running node example.js yields:

import x from "xastscript";
console.log(x("album", {
  id: 123
}, x("name", null, "Born in the U.S.A."), x("artist", null, "Bruce Springsteen"), x("releasedate", {
  date: "1984-04-06"
}, "April 6, 1984")));
console.log(x(null, null, 1 + 1, x("self-closing"), x("x", Object.assign({
  name: true,
  key: "value",
  key: expression
}, spread))));

This package exports the identifier buildJsx. There is no default export.

Turn JSX in tree into function calls: <x /> -> h('x')!

In almost all cases, this utility is the same as the Babel plugin, except that they work on slightly different syntax trees.

Some differences:

• no pure annotations things
• this is not a component: <this> -> h('this'), not h(this)
• namespaces are supported: <a:b c:d> -> h('a:b', {'c:d': true}), which throws by default in Babel or can be turned on with throwIfNamespace
• no useSpread, useBuiltIns, or filter options

• tree (Node) — tree to transform (typically Program)
• options (Options, optional) — configuration

Given, modified, tree (Node).

Configuration (TypeScript type).

👉 Note: you can also configure runtime, importSource, pragma, and pragmaFrag from within files through comments.

Choose the runtime (Runtime, default: 'classic').

Comment form: @jsxRuntime theRuntime.

Place to import jsx, jsxs, jsxDEV, and Fragment from, when the effective runtime is automatic (string, default: 'react').

Comment form: @jsxImportSource theSource.

👉 Note: /jsx-runtime or /jsx-dev-runtime is appended to this provided source. In CJS, that can resolve to a file (as in theSource/jsx-runtime.js), but for ESM an export map needs to be set up to point to files:

// …
"exports": {
  // …
  "./jsx-runtime": "./path/to/jsx-runtime.js",
  "./jsx-dev-runtime": "./path/to/jsx-runtime.js"
  // …

Identifier or member expression to call when the effective runtime is classic (string, default: 'React.createElement').

Comment form: @jsx identifier.

Identifier or member expression to use as a symbol for fragments when the effective runtime is classic (string, default: 'React.Fragment').

Comment form: @jsxFrag identifier.

When in the automatic runtime, whether to import theSource/jsx-dev-runtime.js, use jsxDEV, and pass location info when available (boolean, default: false).

This helps debugging but adds a lot of code that you don’t want in production.

File path to the original source file (string, example: 'path/to/file.js'). Passed in location info to jsxDEV when using the automatic runtime with development: true.

How to transform JSX (TypeScript type).

type Runtime = 'automatic' | 'classic'

To support configuration from comments in Acorn, those comments have to be in the program. This is done by espree but not automatically by acorn:

import {Parser} from 'acorn'
import jsx from 'acorn-jsx'

const doc = '' // To do: get `doc` somehow.

const comments = []
const tree = Parser.extend(jsx()).parse(doc, {onComment: comments})
tree.comments = comments

This package is fully typed with TypeScript. It exports the additional type Options and Runtime.

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.

• syntax-tree/hast-util-to-estree — turn hast (HTML) to estree JSX
• coderaiser/estree-to-babel — turn estree to Babel trees

This package is safe.

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.

MIT © Titus Wormer