385 lines
10 KiB
Markdown
385 lines
10 KiB
Markdown
# unist-util-visit-parents
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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 with a stack of parents.
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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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* [`visitParents(tree[, test], visitor[, reverse])`](#visitparentstree-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 and want to know about
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every parent of each node.
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You can use [`unist-util-visit`][unist-util-visit] if you don’t care about the
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entire stack 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 14.14+ and 16.0+), install with [npm][]:
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```sh
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npm install unist-util-visit-parents
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```
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In Deno with [`esm.sh`][esmsh]:
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```js
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import {visitParents} from 'https://esm.sh/unist-util-visit-parents@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 {visitParents} from 'https://esm.sh/unist-util-visit-parents@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 {visitParents} from 'unist-util-visit-parents'
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import {fromMarkdown} from 'mdast-util-from-markdown'
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const tree = fromMarkdown('Some *emphasis*, **strong**, and `code`.')
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visitParents(tree, 'strong', (node, ancestors) => {
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console.log(node.type, ancestors.map(ancestor => ancestor.type))
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})
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```
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Yields:
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```js
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strong ['root', '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 [`visitParents`][api-visitparents].
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There is no default export.
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### `visitParents(tree[, test], visitor[, reverse])`
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Visit nodes, with ancestral information.
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This algorithm performs *[depth-first][]* *[tree traversal][tree-traversal]*
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in *[preorder][]* (**NLR**) or if `reverse` is given, in *reverse preorder*
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(**NRL**).
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You can choose for which nodes `visitor` is called by passing a `test`.
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For complex tests, you should test yourself in `visitor`, as it will be
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faster and will have improved type information.
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Walking the tree is an intensive task.
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Make use of the return values of the visitor when possible.
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Instead of walking a tree multiple times, walk it once, use
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[`unist-util-is`][unist-util-is] to check if a node matches, and then perform
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different operations.
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You can change the tree.
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See [`Visitor`][api-visitor] for more info.
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###### Parameters
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* `tree` ([`Node`][node])
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— tree to traverse
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* `test` ([`Test`][api-test], optional)
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— [`unist-util-is`][unist-util-is]-compatible test
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* `visitor` ([`Visitor`][api-visitor])
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— handle each node
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* `reverse` (`boolean`, default: `false`)
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— traverse in reverse preorder (NRL) instead of the default preorder (NLR)
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###### Returns
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Nothing (`void`).
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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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###### 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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### `BuildVisitor`
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Build a typed `Visitor` function from a tree and a test (TypeScript type).
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It will infer which values are passed as `node` and which as `parents`.
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###### Type parameters
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* `Tree` ([`Node`][node], default: `Node`)
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— tree type
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* `Check` ([`Test`][api-test], default: `string`)
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— test type
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###### Returns
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[`Visitor`][api-visitor].
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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) (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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### `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 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` (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 an ancestor 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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* `parents` ([`Array<Node>`][node])
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— ancestors 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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###### Type
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```ts
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type VisitorResult =
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| Action
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| ActionTuple
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| Index
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| null
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| undefined
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| void
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```
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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-actiontuple], [`BuildVisitor`][api-buildvisitor],
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[`Index`][api-index], [`Test`][api-test], [`Visitor`][api-visitor], and
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[`VisitorResult`][api-visitorresult].
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## Compatibility
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Projects maintained by the unified collective are compatible with all maintained
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versions of Node.js.
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As of now, that is Node.js 14.14+ and 16.0+.
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Our projects sometimes work with older versions, but this is not guaranteed.
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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 the tree with one parent
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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-parents/workflows/main/badge.svg
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[build]: https://github.com/syntax-tree/unist-util-visit-parents/actions
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[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/unist-util-visit-parents.svg
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[coverage]: https://codecov.io/github/syntax-tree/unist-util-visit-parents
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[downloads-badge]: https://img.shields.io/npm/dm/unist-util-visit-parents.svg
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[downloads]: https://www.npmjs.com/package/unist-util-visit-parents
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[size-badge]: https://img.shields.io/bundlephobia/minzip/unist-util-visit-parents.svg
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[size]: https://bundlephobia.com/result?p=unist-util-visit-parents
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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/HEAD/contributing.md
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[support]: https://github.com/syntax-tree/.github/blob/HEAD/support.md
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[coc]: https://github.com/syntax-tree/.github/blob/HEAD/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#node
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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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[unist-util-visit]: https://github.com/syntax-tree/unist-util-visit
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[unist-util-is]: https://github.com/syntax-tree/unist-util-is
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[api-visitparents]: #visitparentstree-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-actiontuple]: #actiontuple
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[api-buildvisitor]: #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-visitorresult]: #visitorresult
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