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https://github.com/syntax-tree/unist-util-filter

utility to create a new tree with nodes that pass a filter
https://github.com/syntax-tree/unist-util-filter

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utility to create a new tree with nodes that pass a filter

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# unist-util-filter



[![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 create a new tree with only nodes that pass a test.



## Contents



*   [What is this?](#what-is-this)

*   [When should I use this?](#when-should-i-use-this)

*   [Install](#install)

*   [Use](#use)

*   [API](#api)

    *   [`filter(tree[, options][, test])`](#filtertree-options-test)

    *   [`Options`](#options)

*   [Types](#types)

*   [Compatibility](#compatibility)

*   [Related](#related)

*   [Contribute](#contribute)

*   [License](#license)



## What is this?



This is a small utility that helps you clean a tree.



## When should I use this?



You can use this utility to remove things from a tree.

This utility is very similar to [`unist-util-remove`][unist-util-remove], which

changes the given tree.

Modifying a tree like that utility does is much faster on larger documents.



You can also walk the tree with [`unist-util-visit`][unist-util-visit] to remove

nodes.

To create trees, use [`unist-builder`][unist-builder].



## Install



This package is [ESM only][esm].

In Node.js (version 16+), install with [npm][]:



```sh

npm install unist-util-filter

```



In Deno with [`esm.sh`][esmsh]:



```js

import {filter} from 'https://esm.sh/unist-util-filter@5'

```



In browsers with [`esm.sh`][esmsh]:



```html



  import {filter} from 'https://esm.sh/unist-util-filter@5?bundle'



```



## Use



```js

import {u} from 'unist-builder'

import {filter} from 'unist-util-filter'



const tree = u('root', [

  u('leaf', '1'),

  u('parent', [u('leaf', '2'), u('parent', [u('leaf', '3')])]),

  u('leaf', '4')

])



const newTree = filter(tree, node => node.type !== 'leaf' || node.value % 2 === 0)



console.dir(newTree, {depth: null})

```



Yields:



```js

{

  type: 'root',

  children: [

    {type: 'parent', children: [{type: 'leaf', value: '2'}]},

    {type: 'leaf', value: '4'}

  ]

}

```



## API



This package exports the identifier [`filter`][filter].

There is no default export.



### `filter(tree[, options][, test])`



Create a new `tree` of copies of all nodes that pass `test`.



The tree is walked in *[preorder][]* (NLR), visiting the node itself, then its

head, etc.



###### Parameters



*   `tree` ([`Node`][node])

    — tree to filter

*   `options` ([`Options`][options], optional)

    — configuration

*   `test` ([`Test`][test], optional)

    — `unist-util-is` compatible test



###### Returns



New filtered tree ([`Node`][node] or `undefined`).



`undefined` is returned if `tree` itself didn’t pass the test, or is cascaded

away.



### `Options`



Configuration (TypeScript type).



###### Fields



*   `cascade` (`boolean`, default: `true`)

    — whether to drop parent nodes if they had children, but all their

    children were filtered out



## Types



This package is fully typed with [TypeScript][].

It exports the additional type [`Options`][options].



## 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-filter@^5`,

compatible with Node.js 16.



## Related



*   [`unist-util-visit`](https://github.com/syntax-tree/unist-util-visit)

    — walk the tree

*   [`unist-util-visit-parents`](https://github.com/syntax-tree/unist-util-visit-parents)

    — walk the tree with a stack of parents

*   [`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) by a 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] © Eugene Sharygin



[build-badge]: https://github.com/syntax-tree/unist-util-filter/workflows/main/badge.svg



[build]: https://github.com/syntax-tree/unist-util-filter/actions



[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/unist-util-filter.svg



[coverage]: https://codecov.io/github/syntax-tree/unist-util-filter



[downloads-badge]: https://img.shields.io/npm/dm/unist-util-filter.svg



[downloads]: https://www.npmjs.com/package/unist-util-filter



[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=unist-util-filter



[size]: https://bundlejs.com/?q=unist-util-filter



[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



[health]: https://github.com/syntax-tree/.github



[contributing]: https://github.com/syntax-tree/.github/blob/HEAD/contributing.md



[support]: https://github.com/syntax-tree/.github/blob/HEAD/support.md



[coc]: https://github.com/syntax-tree/.github/blob/HEAD/code-of-conduct.md



[unist]: https://github.com/syntax-tree/unist



[node]: https://github.com/syntax-tree/unist#node



[preorder]: https://www.geeksforgeeks.org/tree-traversals-inorder-preorder-and-postorder/



[unist-util-remove]: https://github.com/syntax-tree/unist-util-remove



[unist-util-visit]: https://github.com/syntax-tree/unist-util-visit



[unist-builder]: https://github.com/syntax-tree/unist-builder



[test]: https://github.com/syntax-tree/unist-util-is#test



[filter]: #filtertree-options-test



[options]: #options