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wooorm committed May 18, 2022
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[![Backers][backers-badge]][collective]
[![Chat][chat-badge]][chat]

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

There is currently one project actively maintained that can transform JSX to
function calls: Babel.
Babel is amazing but ginormous (±300kb) and slow.
Switching from it to [estree][] in a project where Babel was only a small part
made the whole project [**68% smaller and 63% faster**][pr].
So let’s make that two implementations.
## Contents

## Install
* [What is this?](#what-is-this)
* [When should I use this?](#when-should-i-use-this)
* [Install](#install)
* [Use](#use)
* [API](#api)
* [`buildJsx(tree, options?)`](#buildjsxtree-options)
* [Examples](#examples)
* [Example: use with Acorn](#example-use-with-acorn)
* [Algorithm](#algorithm)
* [Types](#types)
* [Compatibility](#compatibility)
* [Related](#related)
* [Contribute](#contribute)
* [License](#license)

## What is this?

This package is ESM only: Node 12+ is needed to use it and it must be `import`ed
instead of `require`d.
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.

[npm][]:
## When should I use this?

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

## Install

This package is [ESM only][esm].
In Node.js (version 12.20+, 14.14+, or 16.0+), install with [npm][]:

```sh
npm install estree-util-build-jsx
```

In Deno with [`esm.sh`][esmsh]:

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

In browsers with [`esm.sh`][esmsh]:

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

## Use

Say we have the following file, `example.jsx`:
Say we have the following `example.jsx`:

```js
import x from 'xastscript'
Expand All @@ -52,28 +85,28 @@ console.log(
)
```

And our script, `example.js`, looks as follows:
…and next to it a module `example.js`:

```js
import fs from 'node:fs'
import fs from 'node:fs/promises'
import {Parser} from 'acorn'
import jsx from 'acorn-jsx'
import {generate} from 'astring'
import {buildJsx} from 'estree-util-build-jsx'

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

const tree = Parser.extend(jsx()).parse(doc, {
sourceType: 'module',
ecmaVersion: 2020
ecmaVersion: 2022
})

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

console.log(generate(tree))
```

Now, running `node example` yields:
…now running `node example.js` yields:

```js
import x from 'xastscript';
Expand All @@ -91,32 +124,67 @@ console.log(x(null, null, 1 + 1, x("self-closing"), x("x", Object.assign({

## API

This package exports the following identifiers: `buildJsx`.
This package exports the identifier `buildJsx`.
There is no default export.

### `buildJsx(tree, options?)`

Turn JSX in `tree` ([`Program`][program]) into hyperscript calls.
Turn JSX in `tree` ([`Program`][program]) into function calls:
`<x />` -> `h('x')`!

##### `options`

Configuration (optional).

> 👉 **Note**: you can also configure `runtime`, `importSource`, `pragma`, and
> `pragmaFrag` from within files through comments.
###### `options.runtime`

Choose the [runtime][].
Choose the [runtime][]
(`string`, `'automatic'` or `'classic'`, default: `'classic'`).

Comment form: `@jsxRuntime theRuntime`.

###### `options.importSource`

Place to import `jsx`, `jsxs`, and/or `Fragment` from, when the effective
runtime is automatic (`string`, default: `'react'`).
Comment: `@jsxImportSource theSource`.
Note that `/jsx-runtime` is appended to this provided source.
Place to import `jsx`, `jsxs`, `jsxDEV`, and/or `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:
>
> ```js
> // …
> "exports": {
> // …
> "./jsx-runtime": "./path/to/jsx-runtime.js",
> "./jsx-dev-runtime": "./path/to/jsx-runtime.js"
> // …
> ```
###### `options.pragma`
Identifier or member expression to call when the effective runtime is classic
(`string`, default: `'React.createElement'`).
Comment form: `@jsx identifier`.
###### `options.pragmaFrag`
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`.
##### `options.development`
###### `options.development`
Add location info on where a component originated from (`boolean`, default:
`false`).
Import `jsxDEV` from `theSource/jsx-dev-runtime.js` and add location info on
where a component originated from (`boolean`, default: `false`).
This helps debugging but adds a lot of code that you don’t want in production.
Only used in the automatic runtime.
Expand All @@ -126,58 +194,71 @@ File path to the original source file (`string`, example: `'path/to/file.js'`).
Used in the location info when using the automatic runtime with
`development: true`.
###### `options.pragma`
##### Returns
Identifier or member expression to call when the effective runtime is classic
(`string`, default: `'React.createElement'`).
Comment: `@jsx identifier`.
The given `tree` (`Node`).
###### `options.pragmaFrag`

Identifier or member expression to use as a sumbol for fragments when the
effective runtime is classic (`string`, default: `'React.Fragment'`).
Comment: `@jsxFrag identifier`.
## Examples
###### Returns
### Example: use with Acorn
`Node` — The given `tree`.

###### Notes

To support configuration from comments, those comments have to be in the
program.
This is done automatically by [`espree`][espree].
For [`acorn`][acorn], it can be done like so:
To support configuration from comments in Acorn, those comments have to be in
the program.
This is done by [`espree`][espree] but not automatically by [`acorn`][acorn]:
```js
import {Parser} from 'acorn'
import jsx from 'acorn-jsx'
var doc = ''
const doc = '' // To do: get `doc` somehow.
var comments = []
var tree = Parser.extend(jsx()).parse(doc, {onComment: comments})
const comments = []
const tree = Parser.extend(jsx()).parse(doc, {onComment: comments})
tree.comments = comments
```
## Algorithm
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 or dev things
* 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
## Types
This package is fully typed with [TypeScript][].
It exports the types `Options` and `Node`.
## Compatibility
Projects maintained by the unified collective are compatible with all maintained
versions of Node.js.
As of now, that is Node.js 12.20+, 14.14+, and 16.0+.
Our projects sometimes work with older versions, but this is not guaranteed.
## Related
* [`syntax-tree/hast-util-to-estree`](https://github.com/syntax-tree/hast-util-to-estree)
— Transform [hast](https://github.com/syntax-tree/hast) (HTML) to [estree][]
— turn [hast](https://github.com/syntax-tree/hast) (HTML) to [estree][]
JSX
* [`coderaiser/estree-to-babel`](https://github.com/coderaiser/estree-to-babel)
— Transform [estree][] to Babel trees
— turn [estree][] to Babel trees
## Contribute
See [`contributing.md` in `syntax-tree/.github`][contributing] for ways to get
started.
See [`support.md`][support] for ways to get help.
This project has a [code of conduct][coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.
## License
Expand Down Expand Up @@ -211,12 +292,24 @@ Some differences:
[chat]: https://github.com/syntax-tree/unist/discussions
[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
[npm]: https://docs.npmjs.com/cli/install
[esmsh]: https://esm.sh
[license]: license
[author]: https://wooorm.com
[typescript]: https://www.typescriptlang.org
[contributing]: https://github.com/syntax-tree/.github/blob/main/contributing.md
[support]: https://github.com/syntax-tree/.github/blob/main/support.md
[coc]: https://github.com/syntax-tree/.github/blob/main/code-of-conduct.md
[acorn]: https://github.com/acornjs/acorn
[estree]: https://github.com/estree/estree
Expand All @@ -225,6 +318,8 @@ Some differences:
[program]: https://github.com/estree/estree/blob/master/es5.md#programs
[pr]: https://github.com/mdx-js/mdx/pull/1399

[runtime]: https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html
[swc]: https://swc.rs
[esbuild]: https://esbuild.github.io

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