unist-util-is

unist-util-is

unist utility to check if nodes pass a test.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • is(node[, test[, index, parent[, context]]])
  • convert(test)
  • Check
  • Test
  • TestFunction
• Examples
  • Example of convert
• Types
• Compatibility
• Related
• Contribute
• 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, 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

• node (unknown, optional) — thing to check, typically Node
• test (Test, optional) — a test for a specific element
• index (number, optional) — the node’s position in its parent
• parent (Node, optional) — the node’s parent
• context (unknown, optional) — context object (this) to call test with

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

• test (Test, optional) — a test for a specific node

Returns

A check (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, 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

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:

• when string, checks that the node has that tag name
• when function, see TestFunction
• 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) — a node
• index (number or undefined) — the node’s position in its parent
• parent (Node or undefined) — the node’s parent

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