estree-util-to-js
estree (and esast) utility to serialize estrees as JavaScript.
Contents
What is this?
This package is a utility that turns an estree syntax tree into a string of JavaScript.
When should I use this?
You can use this utility when you want to get the serialized JavaScript that is represented by the syntax tree, either because you’re done with the syntax tree, or because you’re integrating with another tool that does not support syntax trees.
This utility is particularly useful when integrating with other unified tools, such as unist and vfile.
The utility esast-util-from-js does the inverse of this utility. It turns JS into esast.
Install
This package is ESM only. In Node.js (version 16+), install with npm:
npm install estree-util-to-js
In Deno with esm.sh:
import {toJs} from 'https://esm.sh/estree-util-to-js@2'
In browsers with esm.sh:
<script type="module">
import {toJs} from 'https://esm.sh/estree-util-to-js@2?bundle'
</script>
Use
import fs from 'node:fs/promises'
import {parse} from 'acorn'
import {toJs} from 'estree-util-to-js'
const file = String(await fs.readFile('index.js'))
const tree = parse(file, {ecmaVersion: 2022, sourceType: 'module', locations: true})
// @ts-expect-error: acorn is funky but it works fine.
console.log(toJs(tree))
Yields:
{
value: "export {toJs} from './lib/index.js';\nexport {jsx} from './lib/jsx.js';\n",
map: undefined
}
API
This package exports the identifiers jsx and toJs. There is no default export.
toJs(tree[, options])
Serialize an estree as JavaScript.
Parameters
Returns
Result, optionally with source map (Result).
jsx
Map of handlers to handle the nodes of JSX extensions in JavaScript (Handlers).
Handler
Handle a particular node (TypeScript type).
Parameters
this (Generator) — astring generatornode (Node) — node to serializestate (State) — info passed around
Returns
Nothing (undefined).
Handlers
Handlers of nodes (TypeScript type).
Type
type Handlers = Partial<Record<Node['type'], Handler>>
Map
Raw source map from source-map (TypeScript type).
Options
Configuration (TypeScript type).
Fields
SourceMapGenerator (SourceMapGenerator) — generate a source map with this classfilePath (string) — path to original input filehandlers (Handlers) — extra handlers
Result
Result (TypeScript type).
Fields
value (string) — serialized JavaScriptmap (Map or undefined) — source map as (parsed) JSON
State
State from astring (TypeScript type).
Examples
Example: source maps
Source maps are supported when passing the SourceMapGenerator class from source-map. You should also pass filePath. Modified example from § Use above:
import fs from 'node:fs/promises'
import {parse} from 'acorn'
+import {SourceMapGenerator} from 'source-map'
import {toJs} from 'estree-util-to-js'
-const file = String(await fs.readFile('index.js'))
+const filePath = 'index.js'
+const file = String(await fs.readFile(filePath))
const tree = parse(file, {
ecmaVersion: 2022,
@@ -11,4 +13,4 @@ const tree = parse(file, {
})
// @ts-expect-error: acorn is funky but it works fine.
-console.log(toJs(tree))
+console.log(toJs(tree, {filePath, SourceMapGenerator}))
Yields:
{
value: "export {toJs} from './lib/index.js';\nexport {jsx} from './lib/jsx.js';\n",
map: {
version: 3,
sources: [ 'index.js' ],
names: [],
mappings: 'QAOQ,WAAW;QACX,UAAU',
file: 'index.js'
}
}
To get comments to work, they have to be inside the tree. This is not done by Acorn. estree-util-attach-comments can do that. Modified example from § Use above:
import fs from 'node:fs/promises'
import {parse} from 'acorn'
+import {attachComments} from 'estree-util-attach-comments'
import {toJs} from 'estree-util-to-js'
const file = String(await fs.readFile('index.js'))
+/** @type {Array<import('estree-jsx').Comment>} */
+const comments = []
const tree = parse(file, {
ecmaVersion: 2022,
sourceType: 'module',
- locations: true
+ locations: true,
+ // @ts-expect-error: acorn is funky these comments are fine.
+ onComment: comments
})
+attachComments(tree, comments)
// @ts-expect-error: acorn is funky but it works fine.
console.log(toJs(tree))
Yields:
{
value: '/**\n' +
"* @typedef {import('./lib/index.js').Options} Options\n" +
"* @typedef {import('./lib/types.js').Handler} Handler\n" +
"* @typedef {import('./lib/types.js').Handlers} Handlers\n" +
"* @typedef {import('./lib/types.js').State} State\n" +
'*/\n' +
"export {toJs} from './lib/index.js';\n" +
"export {jsx} from './lib/jsx.js';\n",
map: undefined
}
Example: JSX
To get JSX to work, handlers need to be registered. This is not done by default, but they are exported as jsx and can be passed. Modified example from § Use above:
import fs from 'node:fs/promises'
-import {parse} from 'acorn'
-import {toJs} from 'estree-util-to-js'
+import {Parser} from 'acorn'
+import acornJsx from 'acorn-jsx'
+import {jsx, toJs} from 'estree-util-to-js'
-const file = String(await fs.readFile('index.js'))
+const file = '<>{1 + 1}</>'
-const tree = parse(file, {
+const tree = Parser.extend(acornJsx()).parse(file, {
ecmaVersion: 2022,
sourceType: 'module',
locations: true
})
// @ts-expect-error: acorn is funky but it works fine.
-console.log(toJs(tree))
+console.log(toJs(tree, {handlers: jsx}))
Yields:
{ value: '<>{1 + 1}</>;\n', map: undefined }
Types
This package is fully typed with TypeScript. It exports the additional types Handler, Handlers, Map, Options, Result, and State.
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, estree-util-to-js@^2, compatible with Node.js 16.
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