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