unist utility to check if nodes pass a test.

• 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

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

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.

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>

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
}

This package exports the identifiers convert and is. There is no default export.

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

• 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

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

When an incorrect test, index, or parent is given. There is no error thrown when node is not a node.

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.

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

A check (Check).

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

• 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

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

Check for an arbitrary node (TypeScript 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

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

• node (Node) — a node
• index (number or undefined) — the node’s position in its parent
• parent (Node or undefined) — the node’s parent

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

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'}]

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

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.

• unist-util-find-after — find a node after another node
• unist-util-find-before — find a node before another node
• unist-util-find-all-after — find all nodes after another node
• unist-util-find-all-before — find all nodes before another node
• unist-util-find-all-between — find all nodes between two nodes
• unist-util-filter — create a new tree with nodes that pass a check
• unist-util-remove — remove nodes from tree

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.

MIT © Titus Wormer