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# unist-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]
[unist][] utility to walk the tree.
## 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[, test], visitor[, reverse])`](#visittree-test-visitor-reverse)
* [`CONTINUE`](#continue)
* [`EXIT`](#exit)
* [`SKIP`](#skip)
* [`Action`](#action)
* [`ActionTuple`](#actiontuple)
* [`BuildVisitor`](#buildvisitor)
* [`Index`](#index)
* [`Test`](#test)
* [`Visitor`](#visitor)
* [`VisitorResult`](#visitorresult)
* [Types](#types)
* [Compatibility](#compatibility)
* [Related](#related)
* [Contribute](#contribute)
* [License](#license)
## What is this?
This is a very important utility for working with unist as it lets you walk the
tree.
## When should I use this?
You can use this utility when you want to walk the tree.
You can use [`unist-util-visit-parents`][vp] if you care about the entire stack
of parents.
## Install
This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:
```sh
npm install unist-util-visit
```
In Deno with [`esm.sh`][esmsh]:
```js
import {CONTINUE, EXIT, SKIP, visit} from 'https://esm.sh/unist-util-visit@5'
```
In browsers with [`esm.sh`][esmsh]:
```html
<script type="module">
import {CONTINUE, EXIT, SKIP, visit} from 'https://esm.sh/unist-util-visit@5?bundle'
</script>
```
## Use
```js
import {fromMarkdown} from 'mdast-util-from-markdown'
import {visit} from 'unist-util-visit'
const tree = fromMarkdown('Some *emphasis*, **strong**, and `code`.')
visit(tree, 'text', function (node, index, parent) {
console.log([node.value, parent ? parent.type : index])
})
```
Yields:
```js
[ 'Some ', 'paragraph' ]
[ 'emphasis', 'emphasis' ]
[ ', ', 'paragraph' ]
[ 'strong', 'strong' ]
[ ', and ', 'paragraph' ]
[ '.', 'paragraph' ]
```
## API
This package exports the identifiers [`CONTINUE`][api-continue],
[`EXIT`][api-exit], [`SKIP`][api-skip], and [`visit`][api-visit].
There is no default export.
### `visit(tree[, test], visitor[, reverse])`
This function works exactly the same as [`unist-util-visit-parents`][vp],
but [`Visitor`][api-visitor] has a different signature.
### `CONTINUE`
Continue traversing as normal (`true`).
### `EXIT`
Stop traversing immediately (`false`).
### `SKIP`
Do not traverse this node’s children (`'skip'`).
### `Action`
Union of the action types (TypeScript type).
See [`Action` in `unist-util-visit-parents`][vp-action].
### `ActionTuple`
List with an action and an index (TypeScript type).
See [`ActionTuple` in `unist-util-visit-parents`][vp-action-tuple].
### `BuildVisitor`
Build a typed `Visitor` function from a tree and a test (TypeScript type).
See [`BuildVisitor` in `unist-util-visit-parents`][vp-build-visitor].
### `Index`
Move to the sibling at `index` next (TypeScript type).
See [`Index` in `unist-util-visit-parents`][vp-index].
### `Test`
[`unist-util-is`][unist-util-is] compatible test (TypeScript type).
### `Visitor`
Handle a node (matching `test`, if given) (TypeScript type).
Visitors are free to transform `node`.
They can also transform `parent`.
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` (or next siblings, in
case of reverse), the `Visitor` should return a new `Index` to specify the
sibling to traverse after `node` is traversed.
Adding or removing next siblings of `node` (or previous siblings, in case
of reverse) is handled as expected without needing to return a new `Index`.
Removing the children property of `parent` still results in them being
traversed.
###### Parameters
* `node` ([`Node`][node])
— found node
* `index` (`number` or `undefined`)
— index of `node` in `parent`
* `parent` ([`Node`][node] or `undefined`)
— parent of `node`
###### Returns
What to do next.
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.
### `VisitorResult`
Any value that can be returned from a visitor (TypeScript type).
See [`VisitorResult` in `unist-util-visit-parents`][vp-visitor-result].
## Types
This package is fully typed with [TypeScript][].
It exports the additional types [`Action`][api-action],
[`ActionTuple`][api-action-tuple], [`BuildVisitor`][api-build-visitor],
[`Index`][api-index], [`Test`][api-test], [`Visitor`][api-visitor], and
[`VisitorResult`][api-visitor-result].
## 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, `unist-util-visit@^5`,
compatible with Node.js 16.
## Related
* [`unist-util-visit-parents`][vp]
— walk the tree with a stack of parents
* [`unist-util-filter`](https://github.com/syntax-tree/unist-util-filter)
— create a new tree with all nodes that pass a test
* [`unist-util-map`](https://github.com/syntax-tree/unist-util-map)
— create a new tree with all nodes mapped by a given function
* [`unist-util-flatmap`](https://gitlab.com/staltz/unist-util-flatmap)
— create a new tree by mapping (to an array) with the given function
* [`unist-util-remove`](https://github.com/syntax-tree/unist-util-remove)
— remove nodes from a tree that pass a test
* [`unist-util-select`](https://github.com/syntax-tree/unist-util-select)
— select nodes with CSS-like selectors
## 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/unist-util-visit/workflows/main/badge.svg
[build]: https://github.com/syntax-tree/unist-util-visit/actions
[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/unist-util-visit.svg
[coverage]: https://codecov.io/github/syntax-tree/unist-util-visit
[downloads-badge]: https://img.shields.io/npm/dm/unist-util-visit.svg
[downloads]: https://www.npmjs.com/package/unist-util-visit
[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=unist-util-visit
[size]: https://bundlejs.com/?q=unist-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
[unist]: https://github.com/syntax-tree/unist
[node]: https://github.com/syntax-tree/unist#nodes
[unist-util-is]: https://github.com/syntax-tree/unist-util-is
[vp]: https://github.com/syntax-tree/unist-util-visit-parents
[vp-action]: https://github.com/syntax-tree/unist-util-visit-parents#action
[vp-action-tuple]: https://github.com/syntax-tree/unist-util-visit-parents#actiontuple
[vp-build-visitor]: https://github.com/syntax-tree/unist-util-visit-parents#buildvisitor
[vp-index]: https://github.com/syntax-tree/unist-util-visit-parents#index
[vp-visitor-result]: https://github.com/syntax-tree/unist-util-visit-parents#visitorresult
[api-visit]: #visittree-test-visitor-reverse
[api-continue]: #continue
[api-exit]: #exit
[api-skip]: #skip
[api-action]: #action
[api-action-tuple]: #actiontuple
[api-build-visitor]: #buildvisitor
[api-index]: #index
[api-test]: #test
[api-visitor]: #visitor
[api-visitor-result]: #visitorresult