360 lines
8.7 KiB
Markdown
Executable File
360 lines
8.7 KiB
Markdown
Executable File
# estree-util-visit
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[![Build][build-badge]][build]
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[![Coverage][coverage-badge]][coverage]
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[![Downloads][downloads-badge]][downloads]
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[![Size][size-badge]][size]
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[![Sponsors][sponsors-badge]][collective]
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[![Backers][backers-badge]][collective]
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[![Chat][chat-badge]][chat]
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[estree][] (and [esast][]) utility to visit nodes.
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## Contents
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* [What is this?](#what-is-this)
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* [When should I use this?](#when-should-i-use-this)
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* [Install](#install)
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* [Use](#use)
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* [API](#api)
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* [`visit(tree, visitor|visitors)`](#visittree-visitorvisitors)
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* [`CONTINUE`](#continue)
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* [`EXIT`](#exit)
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* [`SKIP`](#skip)
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* [`Action`](#action)
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* [`ActionTuple`](#actiontuple)
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* [`Index`](#index)
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* [`Visitor`](#visitor)
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* [`Visitors`](#visitors)
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* [Types](#types)
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* [Compatibility](#compatibility)
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* [Related](#related)
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* [Contribute](#contribute)
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* [License](#license)
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## What is this?
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This package is a utility that helps you walk the tree.
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## When should I use this?
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This package helps when dealing with JavaScript ASTs.
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Use [`unist-util-visit`][unist-util-visit] for other unist ASTs.
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## Install
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This package is [ESM only][esm].
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In Node.js (version 16+), install with [npm][]:
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```sh
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npm install estree-util-visit
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```
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In Deno with [`esm.sh`][esmsh]:
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```js
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import {visit} from 'https://esm.sh/estree-util-visit@2'
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```
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In browsers with [`esm.sh`][esmsh]:
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```html
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<script type="module">
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import {visit} from 'https://esm.sh/estree-util-visit@2?bundle'
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</script>
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```
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## Use
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```js
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import {parse} from 'acorn'
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import {visit} from 'estree-util-visit'
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const tree = parse(
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'export function x() { console.log(1 + "2"); process.exit(3) }',
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{sourceType: 'module', ecmaVersion: 2020}
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)
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visit(tree, function (node) {
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if (node.type === 'Literal' && 'value' in node) console.log(node.value)
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})
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// Both enter and leave:
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walk(tree, {
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enter(node, field, index, parents) { /* … */ },
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leave(node, field, index, parents) { /* … */ }
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})
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```
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Yields:
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```txt
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1
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"2"
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3
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```
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## API
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This package exports the identifiers [`CONTINUE`][api-continue],
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[`EXIT`][api-exit],
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[`SKIP`][api-skip], and
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[`visit`][api-visit].
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There is no default export.
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### `visit(tree, visitor|visitors)`
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Visit nodes, with ancestral information.
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This algorithm performs [*depth-first*][depth-first]
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[*tree traversal*][tree-traversal] in [*preorder*][preorder] (**NLR**) and/or
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[*postorder*][postorder] (**LRN**).
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Compared to other estree walkers, this does not need a dictionary of which
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fields are nodes, because it ducktypes instead.
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Walking the tree is an intensive task.
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Make use of the return values of the visitor(s) when possible.
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Instead of walking a tree multiple times, walk it once, use
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[`unist-util-is`][is] to check if a node matches, and then perform different
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operations.
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###### Parameters
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* `tree` ([`Node`][node])
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— tree to traverse
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* `visitor` ([`Visitor`][api-visitor])
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— same as passing `{enter: visitor}`
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* `visitors` ([`Visitors`][api-visitors])
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— handle each node
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###### Returns
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Nothing (`undefined`).
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### `CONTINUE`
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Continue traversing as normal (`symbol`).
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### `EXIT`
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Stop traversing immediately (`symbol`).
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### `SKIP`
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Do not traverse this node’s children (`symbol`).
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### `Action`
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Union of the action types (TypeScript type).
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###### Type
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```ts
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type Action = typeof CONTINUE | typeof EXIT | typeof SKIP
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```
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### `ActionTuple`
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List with one or two values, the first an action, the second an index
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(TypeScript type).
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###### Type
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```ts
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type ActionTuple = [
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(Action | null | undefined | void)?,
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(Index | null | undefined)?
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]
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```
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### `Index`
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Move to the sibling at `index` next (after node itself is completely
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traversed), when moving in an array (TypeScript type).
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Useful if mutating the tree, such as removing the node the visitor is currently
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on, or any of its previous siblings.
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Results less than 0 or greater than or equal to `children.length` stop
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traversing the parent.
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###### Type
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```ts
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type Index = number
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```
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### `Visitor`
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Handle a node (TypeScript type).
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Visitors are free to transform `node`.
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They can also transform the parent of node (the last of `ancestors`).
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Replacing `node` itself, if `SKIP` is not returned, still causes its
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descendants to be walked (which is a bug).
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When adding or removing previous siblings of `node`, the `Visitor` should
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return a new `Index` to specify the sibling to traverse after `node` is
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traversed.
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Adding or removing next siblings of `node` is handled as expected without
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needing to return a new `Index`.
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###### Parameters
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* `node` ([`Node`][node])
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— found node
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* `key` (`string` or `undefined`)
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— field at which `node` lives in its parent (or where a list of nodes
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lives)
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* `index` (`number` or `undefined`)
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— index where `node` lives if `parent[key]` is an array
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* `ancestors` ([`Array<Node>`][node])
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— ancestors of `node`
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###### Returns
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What to do next ([`Action`][api-action], [`Index`][api-index], or
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[`ActionTuple`][api-action-tuple], optional).
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An `Index` is treated as a tuple of `[CONTINUE, Index]`.
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An `Action` is treated as a tuple of `[Action]`.
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Passing a tuple back only makes sense if the `Action` is `SKIP`.
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When the `Action` is `EXIT`, that action can be returned.
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When the `Action` is `CONTINUE`, `Index` can be returned.
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### `Visitors`
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Handle nodes when entering (preorder) and leaving (postorder) (TypeScript
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type).
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###### Fields
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* `enter` ([`Visitor`][api-visitor], optional)
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— handle nodes when entering (preorder)
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* `leave` ([`Visitor`][api-visitor], optional)
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— handle nodes when leaving (postorder)
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## Types
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This package is fully typed with [TypeScript][].
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It exports the additional types [`Action`][api-action],
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[`ActionTuple`][api-action-tuple],
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[`Index`][api-index],
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[`Visitor`][api-visitor], and
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[`Visitors`][api-visitors].
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## Compatibility
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Projects maintained by the unified collective are compatible with maintained
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versions of Node.js.
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When we cut a new major release, we drop support for unmaintained versions of
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Node.
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This means we try to keep the current release line, `estree-util-visit@^2`,
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compatible with Node.js 16.
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## Related
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* [`unist-util-visit`](https://github.com/syntax-tree/unist-util-visit)
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— walk any unist tree
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## Contribute
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See [`contributing.md`][contributing] in [`syntax-tree/.github`][health] for
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ways to get started.
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See [`support.md`][support] for ways to get help.
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This project has a [code of conduct][coc].
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By interacting with this repository, organization, or community you agree to
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abide by its terms.
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## License
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[MIT][license] © [Titus Wormer][author]
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<!-- Definition -->
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[build-badge]: https://github.com/syntax-tree/estree-util-visit/workflows/main/badge.svg
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[build]: https://github.com/syntax-tree/estree-util-visit/actions
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[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/estree-util-visit.svg
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[coverage]: https://codecov.io/github/syntax-tree/estree-util-visit
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[downloads-badge]: https://img.shields.io/npm/dm/estree-util-visit.svg
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[downloads]: https://www.npmjs.com/package/estree-util-visit
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[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=estree-util-visit
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[size]: https://bundlejs.com/?q=estree-util-visit
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[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
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[backers-badge]: https://opencollective.com/unified/backers/badge.svg
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[collective]: https://opencollective.com/unified
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[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
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[chat]: https://github.com/syntax-tree/unist/discussions
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[npm]: https://docs.npmjs.com/cli/install
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[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
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[esmsh]: https://esm.sh
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[typescript]: https://www.typescriptlang.org
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[license]: license
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[author]: https://wooorm.com
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[health]: https://github.com/syntax-tree/.github
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[contributing]: https://github.com/syntax-tree/.github/blob/main/contributing.md
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[support]: https://github.com/syntax-tree/.github/blob/main/support.md
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[coc]: https://github.com/syntax-tree/.github/blob/main/code-of-conduct.md
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[esast]: https://github.com/syntax-tree/esast
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[estree]: https://github.com/estree/estree
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[depth-first]: https://github.com/syntax-tree/unist#depth-first-traversal
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[tree-traversal]: https://github.com/syntax-tree/unist#tree-traversal
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[preorder]: https://github.com/syntax-tree/unist#preorder
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[postorder]: https://github.com/syntax-tree/unist#postorder
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[is]: https://github.com/syntax-tree/unist-util-is
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[node]: https://github.com/syntax-tree/esast#node
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[unist-util-visit]: https://github.com/syntax-tree/unist-util-visit
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[api-continue]: #continue
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[api-action]: #action
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[api-action-tuple]: #actiontuple
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[api-exit]: #exit
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[api-index]: #index
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[api-skip]: #skip
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[api-visit]: #visittree-visitorvisitors
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[api-visitor]: #visitor
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[api-visitors]: #visitors
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