352 lines
8.5 KiB
Markdown
352 lines
8.5 KiB
Markdown
# estree-util-visit
|
||
|
||
[![Build][build-badge]][build]
|
||
[![Coverage][coverage-badge]][coverage]
|
||
[![Downloads][downloads-badge]][downloads]
|
||
[![Size][size-badge]][size]
|
||
[![Sponsors][sponsors-badge]][collective]
|
||
[![Backers][backers-badge]][collective]
|
||
[![Chat][chat-badge]][chat]
|
||
|
||
[estree][] (and [esast][]) utility to visit nodes.
|
||
|
||
## Contents
|
||
|
||
* [What is this?](#what-is-this)
|
||
* [When should I use this?](#when-should-i-use-this)
|
||
* [Install](#install)
|
||
* [Use](#use)
|
||
* [API](#api)
|
||
* [`visit(tree, visitor|visitors)`](#visittree-visitorvisitors)
|
||
* [`CONTINUE`](#continue)
|
||
* [`EXIT`](#exit)
|
||
* [`SKIP`](#skip)
|
||
* [`Action`](#action)
|
||
* [`ActionTuple`](#actiontuple)
|
||
* [`Index`](#index)
|
||
* [`Visitor`](#visitor)
|
||
* [`Visitors`](#visitors)
|
||
* [Types](#types)
|
||
* [Compatibility](#compatibility)
|
||
* [Related](#related)
|
||
* [Contribute](#contribute)
|
||
* [License](#license)
|
||
|
||
## What is this?
|
||
|
||
This package is a utility that helps you walk the tree.
|
||
|
||
## When should I use this?
|
||
|
||
This package helps when dealing with JavaScript ASTs.
|
||
Use [`unist-util-visit`][unist-util-visit] for other unist ASTs.
|
||
|
||
## Install
|
||
|
||
This package is [ESM only][esm].
|
||
In Node.js (version 14.14+ and 16.0+), install with [npm][]:
|
||
|
||
```sh
|
||
npm install estree-util-visit
|
||
```
|
||
|
||
In Deno with [`esm.sh`][esmsh]:
|
||
|
||
```js
|
||
import {visit} from 'https://esm.sh/estree-util-visit@1'
|
||
```
|
||
|
||
In browsers with [`esm.sh`][esmsh]:
|
||
|
||
```html
|
||
<script type="module">
|
||
import {visit} from 'https://esm.sh/estree-util-visit@1?bundle'
|
||
</script>
|
||
```
|
||
|
||
## Use
|
||
|
||
```js
|
||
import {parse} from 'acorn'
|
||
import {visit} from 'estree-util-visit'
|
||
|
||
const tree = parse(
|
||
'export function x() { console.log(1 + "2"); process.exit(3) }',
|
||
{sourceType: 'module', ecmaVersion: 2020}
|
||
)
|
||
|
||
visit(tree, (node) => {
|
||
if (node.type === 'Literal' && 'value' in node) console.log(node.value)
|
||
})
|
||
|
||
// Both enter and leave:
|
||
walk(tree, {
|
||
enter(node, field, index, parents) { /* … */ },
|
||
leave(node, field, index, parents) { /* … */ }
|
||
})
|
||
```
|
||
|
||
Yields:
|
||
|
||
```txt
|
||
1
|
||
"2"
|
||
3
|
||
```
|
||
|
||
## API
|
||
|
||
This package exports the identifiers [`CONTINUE`][continue], [`EXIT`][exit],
|
||
[`SKIP`][skip], and [`visit`][visit].
|
||
There is no default export.
|
||
|
||
### `visit(tree, visitor|visitors)`
|
||
|
||
Visit nodes, with ancestral information.
|
||
|
||
This algorithm performs [*depth-first*][depth-first]
|
||
[*tree traversal*][tree-traversal] in [*preorder*][preorder] (**NLR**) and/or
|
||
[*postorder*][postorder] (**LRN**).
|
||
|
||
Compared to other estree walkers, this does not need a dictionary of which
|
||
fields are nodes, because it ducktypes instead.
|
||
|
||
Walking the tree is an intensive task.
|
||
Make use of the return values of the visitor(s) when possible.
|
||
Instead of walking a tree multiple times, walk it once, use
|
||
[`unist-util-is`][is] to check if a node matches, and then perform different
|
||
operations.
|
||
|
||
###### Parameters
|
||
|
||
* `tree` ([`Node`][node])
|
||
— tree to traverse
|
||
* `visitor` ([`Visitor`][visitor])
|
||
— same as passing `{enter: visitor}`
|
||
* `visitors` ([`Visitors`][visitors])
|
||
— handle each node
|
||
|
||
###### Returns
|
||
|
||
Nothing (`void`).
|
||
|
||
### `CONTINUE`
|
||
|
||
Continue traversing as normal (`symbol`).
|
||
|
||
### `EXIT`
|
||
|
||
Stop traversing immediately (`symbol`).
|
||
|
||
### `SKIP`
|
||
|
||
Do not traverse this node’s children (`symbol`).
|
||
|
||
### `Action`
|
||
|
||
Union of the action types (TypeScript type).
|
||
|
||
###### Type
|
||
|
||
```ts
|
||
type Action = typeof CONTINUE | typeof SKIP | typeof EXIT
|
||
```
|
||
|
||
### `ActionTuple`
|
||
|
||
List with one or two values, the first an action, the second an index
|
||
(TypeScript type).
|
||
|
||
###### Type
|
||
|
||
```ts
|
||
type ActionTuple = [
|
||
(Action | null | undefined | void)?,
|
||
(Index | null | undefined)?
|
||
]
|
||
```
|
||
|
||
### `Index`
|
||
|
||
Move to the sibling at `index` next (after node itself is completely
|
||
traversed), when moving in an array (TypeScript type).
|
||
|
||
Useful if mutating the tree, such as removing the node the visitor is currently
|
||
on, or any of its previous siblings.
|
||
Results less than 0 or greater than or equal to `children.length` stop
|
||
traversing the parent.
|
||
|
||
###### Type
|
||
|
||
```ts
|
||
type Index = number
|
||
```
|
||
|
||
### `Visitor`
|
||
|
||
Handle a node (TypeScript type).
|
||
|
||
Visitors are free to transform `node`.
|
||
They can also transform the parent of node (the last of `ancestors`).
|
||
|
||
Replacing `node` itself, if `SKIP` is not returned, still causes its
|
||
descendants to be walked (which is a bug).
|
||
|
||
When adding or removing previous siblings of `node`, the `Visitor` should
|
||
return a new `Index` to specify the sibling to traverse after `node` is
|
||
traversed.
|
||
Adding or removing next siblings of `node` is handled as expected without
|
||
needing to return a new `Index`.
|
||
|
||
###### Parameters
|
||
|
||
* `node` ([`Node`][node])
|
||
— found node
|
||
* `key` (`string` or `null`)
|
||
— field at which `node` lives in its parent (or where a list of nodes
|
||
lives)
|
||
* `index` (`number` or `null`)
|
||
— index where `node` lives if `parent[key]` is an array
|
||
* `ancestors` ([`Array<Node>`][node])
|
||
— ancestors of `node`
|
||
|
||
###### Returns
|
||
|
||
What to do next ([`Action`][action], [`Index`][index], or
|
||
[`ActionTuple`][actiontuple], optional).
|
||
|
||
An `Index` is treated as a tuple of `[CONTINUE, Index]`.
|
||
An `Action` is treated as a tuple of `[Action]`.
|
||
|
||
Passing a tuple back only makes sense if the `Action` is `SKIP`.
|
||
When the `Action` is `EXIT`, that action can be returned.
|
||
When the `Action` is `CONTINUE`, `Index` can be returned.
|
||
|
||
### `Visitors`
|
||
|
||
Handle nodes when entering (preorder) and leaving (postorder) (TypeScript
|
||
type).
|
||
|
||
###### Fields
|
||
|
||
* `enter` ([`Visitor`][visitor], optional)
|
||
— handle nodes when entering (preorder)
|
||
* `leave` ([`Visitor`][visitor], optional)
|
||
— handle nodes when leaving (postorder)
|
||
|
||
## Types
|
||
|
||
This package is fully typed with [TypeScript][].
|
||
It exports the additional types [`Action`][action],
|
||
[`ActionTuple`][actiontuple], [`Index`][index],
|
||
[`Visitor`][visitor], and [`Visitors`][visitors].
|
||
|
||
## 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+, 16.0+, and 18.0+.
|
||
Our projects sometimes work with older versions, but this is not guaranteed.
|
||
|
||
## Related
|
||
|
||
* [`unist-util-visit`](https://github.com/syntax-tree/unist-util-visit)
|
||
— walk any unist tree
|
||
|
||
## Contribute
|
||
|
||
See [`contributing.md`][contributing] in [`syntax-tree/.github`][health] 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
|
||
|
||
[MIT][license] © [Titus Wormer][author]
|
||
|
||
<!-- Definition -->
|
||
|
||
[build-badge]: https://github.com/syntax-tree/estree-util-visit/workflows/main/badge.svg
|
||
|
||
[build]: https://github.com/syntax-tree/estree-util-visit/actions
|
||
|
||
[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/estree-util-visit.svg
|
||
|
||
[coverage]: https://codecov.io/github/syntax-tree/estree-util-visit
|
||
|
||
[downloads-badge]: https://img.shields.io/npm/dm/estree-util-visit.svg
|
||
|
||
[downloads]: https://www.npmjs.com/package/estree-util-visit
|
||
|
||
[size-badge]: https://img.shields.io/bundlephobia/minzip/estree-util-visit.svg
|
||
|
||
[size]: https://bundlephobia.com/result?p=estree-util-visit
|
||
|
||
[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
|
||
|
||
[backers-badge]: https://opencollective.com/unified/backers/badge.svg
|
||
|
||
[collective]: https://opencollective.com/unified
|
||
|
||
[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
|
||
|
||
[chat]: https://github.com/syntax-tree/unist/discussions
|
||
|
||
[npm]: https://docs.npmjs.com/cli/install
|
||
|
||
[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
|
||
|
||
[esmsh]: https://esm.sh
|
||
|
||
[typescript]: https://www.typescriptlang.org
|
||
|
||
[license]: license
|
||
|
||
[author]: https://wooorm.com
|
||
|
||
[health]: https://github.com/syntax-tree/.github
|
||
|
||
[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
|
||
|
||
[esast]: https://github.com/syntax-tree/esast
|
||
|
||
[estree]: https://github.com/estree/estree
|
||
|
||
[depth-first]: https://github.com/syntax-tree/unist#depth-first-traversal
|
||
|
||
[tree-traversal]: https://github.com/syntax-tree/unist#tree-traversal
|
||
|
||
[preorder]: https://github.com/syntax-tree/unist#preorder
|
||
|
||
[postorder]: https://github.com/syntax-tree/unist#postorder
|
||
|
||
[is]: https://github.com/syntax-tree/unist-util-is
|
||
|
||
[node]: https://github.com/syntax-tree/esast#node
|
||
|
||
[unist-util-visit]: https://github.com/syntax-tree/unist-util-visit
|
||
|
||
[continue]: #continue
|
||
|
||
[exit]: #exit
|
||
|
||
[skip]: #skip
|
||
|
||
[visit]: #visittree-visitorvisitors
|
||
|
||
[visitor]: #visitor
|
||
|
||
[visitors]: #visitors
|
||
|
||
[action]: #action
|
||
|
||
[index]: #index
|
||
|
||
[actiontuple]: #actiontuple
|