unist utility to check if a node passes a test

Usage no npm install needed!

<script type="module">
  import unistUtilIs from 'https://cdn.skypack.dev/unist-util-is';



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unist utility to check if a node passes a test.


This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.


npm install unist-util-is


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

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

function test(node, n) {
  return n === 5

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


This package exports the following identifiers: is, convert. There is no default export.

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

  • node (Node) — Node to check.
  • test (Function, string, Object, or Array.<Test>, optional) — When nullish, checks if node is a Node. When string, works like passing node => node.type === test. When array, checks if any one of the subtests pass. When object, checks that all keys in test are in node, and that they have strictly equal values
  • index (number, optional) — Index of node in parent
  • parent (Node, optional) — Parent of node
  • context (*, optional) — Context object to invoke test with

boolean — Whether test passed and node is a Node (object with type set to a non-empty string).

function test(node[, index, parent])

  • node (Node) — Node to check
  • index (number?) — Index of node in parent
  • parent (Node?) — Parent of node

* — The to is given context.


boolean? — Whether node matches.


Create a test function from test, that can later be called with a node, index, and parent. Useful if you’re going to test many nodes, for example when creating a utility where something else passes an is-compatible test.

The created function is slightly faster because it expects valid input only. Therefore, passing invalid input, yields unexpected results.

For example:

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

var test = convert('leaf')

var tree = u('tree', [
  u('node', [u('leaf', '1')]),
  u('leaf', '2'),
  u('node', [u('leaf', '3'), u('leaf', '4')]),
  u('leaf', '5')

var leafs = tree.children.filter((child, index) => test(child, index, tree))



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



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