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unist utility to check if nodes pass a test.

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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, works on hast elements.

For more advanced tests, unist-util-select can be used to match against CSS selectors.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install unist-util-is

In Deno with esm.sh:

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

In browsers with esm.sh:

<script type="module">
  import {is} from 'https://esm.sh/unist-util-is@6?bundle'
</script>

Use

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 and 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
Returns

Whether node is a 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
Returns

A check (Check).

Check

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

Parameters
Returns

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

Test

Check for an arbitrary node (TypeScript type).

Type
type Test =
  | Array<Record<string, unknown> | TestFunction | string>
  | Record<string, unknown>
  | TestFunction
  | string
  | null
  | undefined

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

TestFunction

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

Parameters
Returns

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

Examples

Example of convert

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:

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

Types

This package is fully typed with TypeScript. It exports the additional types Check, Test, TestFunction.

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

Contribute

See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Titus Wormer

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