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

utility to check if a node passes a test
https://github.com/syntax-tree/unist-util-is

equal equality is syntax-tree unist unist-util util

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utility to check if a node passes a test

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# unist-util-is



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[![Downloads][downloads-badge]][downloads]

[![Size][size-badge]][size]

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[unist][] utility to check if nodes 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)

  * [`is(node[, test[, index, parent[, context]]])`](#isnode-test-index-parent-context)

  * [`convert(test)`](#converttest)

  * [`Check`](#check)

  * [`Test`](#test)

  * [`TestFunction`](#testfunction)

* [Examples](#examples)

  * [Example of `convert`](#example-of-convert)

* [Types](#types)

* [Compatibility](#compatibility)

* [Related](#related)

* [Contribute](#contribute)

* [License](#license)



## What is this?



This package is a small utility that checks that a node is a certain node.



## When should I use this?



Use this small utility if you find yourself repeating code for checking what

nodes are.



A similar package, [`hast-util-is-element`][hast-util-is-element], works on hast

elements.



For more advanced tests, [`unist-util-select`][unist-util-select] can be used

to match against CSS selectors.



## Install



This package is [ESM only][esm].

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



```sh

npm install unist-util-is

```



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



```js

import {is} from 'https://esm.sh/unist-util-is@6'

```



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



```html



  import {is} from 'https://esm.sh/unist-util-is@6?bundle'



```



## Use



```js

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



const node = {type: 'strong'}

const parent = {type: 'paragraph', children: [node]}



is() // => false

is({children: []}) // => false

is(node) // => true

is(node, 'strong') // => true

is(node, 'emphasis') // => false



is(node, node) // => true

is(parent, {type: 'paragraph'}) // => true

is(parent, {type: 'strong'}) // => false



is(node, test) // => false

is(node, test, 4, parent) // => false

is(node, test, 5, parent) // => true



function test(node, n) {

  return n === 5

}

```



## API



This package exports the identifiers [`convert`][api-convert] and

[`is`][api-is].

There is no default export.



### `is(node[, test[, index, parent[, context]]])`



Check if `node` is a `Node` and whether it passes the given test.



###### Parameters



* `node` (`unknown`, optional)

  — thing to check, typically [`Node`][node]

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

  — a test for a specific element

* `index` (`number`, optional)

  — the node’s position in its parent

* `parent` ([`Node`][node], optional)

  — the node’s parent

* `context` (`unknown`, optional)

  — context object (`this`) to call `test` with



###### Returns



Whether `node` is a [`Node`][node] and passes a test (`boolean`).



###### Throws



When an incorrect `test`, `index`, or `parent` is given.

There is no error thrown when `node` is not a node.



### `convert(test)`



Generate a check from a test.



Useful if you’re going to test many nodes, for example when creating a

utility where something else passes a compatible test.



The created function is a bit faster because it expects valid input only:

a `node`, `index`, and `parent`.



###### Parameters



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

  — a test for a specific node



###### Returns



A check ([`Check`][api-check]).



### `Check`



Check that an arbitrary value is a node (TypeScript type).



###### Parameters



* `this` (`unknown`, optional)

  — context object (`this`) to call `test` with

* `node` (`unknown`)

  — anything (typically a node)

* `index` (`number`, optional)

  — the node’s position in its parent

* `parent` ([`Node`][node], optional)

  — the node’s parent



###### Returns



Whether this is a node and passes a test (`boolean`).



### `Test`



Check for an arbitrary node (TypeScript type).



###### Type



```ts

type Test =

  | Array | TestFunction | string>

  | Record

  | TestFunction

  | string

  | null

  | undefined

```



Checks that the given thing is a node, and then:



* when `string`, checks that the node has that tag name

* when `function`, see  [`TestFunction`][api-test-function]

* when `object`, checks that all keys in test are in node, and that they have

  (strictly) equal values

* when `Array`, checks if one of the subtests pass



### `TestFunction`



Check if a node passes a test (TypeScript type).



###### Parameters



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

  — a node

* `index` (`number` or `undefined`)

  — the node’s position in its parent

* `parent` ([`Node`][node] or `undefined`)

  — the node’s parent



###### Returns



Whether this node passes the test (`boolean`, optional).



## Examples



### Example of `convert`



```js

import {u} from 'unist-builder'

import {convert} from 'unist-util-is'



const test = convert('leaf')



const tree = u('tree', [

  u('node', [u('leaf', '1')]),

  u('leaf', '2'),

  u('node', [u('leaf', '3'), u('leaf', '4')]),

  u('leaf', '5')

])



const leafs = tree.children.filter(function (child, index) {

  return test(child, index, tree)

})



console.log(leafs)

```



Yields:



```js

[{type: 'leaf', value: '2'}, {type: 'leaf', value: '5'}]

```



## Types



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

It exports the additional types [`Check`][api-check],

[`Test`][api-test],

[`TestFunction`][api-test-function].



## 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-is@^6`,

compatible with Node.js 16.



## Related



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

  — find a node after another node

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

  — find a node before another node

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

  — find all nodes after another node

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

  — find all nodes before another node

* [`unist-util-find-all-between`](https://github.com/mrzmmr/unist-util-find-all-between)

  — find all nodes between two nodes

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

  — create a new tree with nodes that pass a check

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

  — remove nodes from tree



## 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]



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



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



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



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



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



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



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



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



[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#node



[hast-util-is-element]: https://github.com/syntax-tree/hast-util-is-element



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



[api-convert]: #converttest



[api-is]: #isnode-test-index-parent-context



[api-check]: #check



[api-test]: #test



[api-test-function]: #testfunction