unist-util-is

What is unist-util-is?

The unist-util-is npm package is a utility library for working with Unist nodes. Unist (Universal Syntax Tree) is part of the unified ecosystem, which provides a way to work with syntax trees for content such as Markdown, HTML, or plain text. unist-util-is specifically helps in testing and filtering nodes in these trees based on certain conditions.

What are unist-util-is's main functionalities?

Test nodes with a condition

This feature allows you to test if a node matches a specific type or condition. In the example, `is` is used to check if the root node is a 'leaf' (which it isn't), and then if the first child of the root is a 'leaf' (which it is).

const is = require('unist-util-is');
const u = require('unist-builder');

const tree = u('root', [
  u('leaf', 'first leaf'),
  u('node', [u('leaf', 'nested leaf')])
]);

const test = is(tree, 'leaf'); // false
const testLeaf = is(tree.children[0], 'leaf'); // true

Filter nodes by type

This feature demonstrates how to filter nodes by type using `is` in combination with `unist-util-select`. It selects all 'leaf' nodes from the tree and filters them to ensure they are of type 'leaf'.

const is = require('unist-util-is');
const u = require('unist-builder');
const select = require('unist-util-select');

const tree = u('root', [
  u('leaf', 'first leaf'),
  u('node', [u('leaf', 'nested leaf')])
]);

const leaves = select.selectAll('leaf', tree).filter(node => is(node, 'leaf'));

Other packages similar to unist-util-is

unist-util-visit

This package is similar to unist-util-is in that it is used to work with Unist nodes. However, unist-util-visit focuses on visiting nodes within a tree, optionally filtering nodes, and applying a function to each node. It differs from unist-util-is by providing traversal capabilities rather than just testing or filtering.

unist-util-select

unist-util-select is used to select nodes from a Unist tree using CSS-like selectors. It complements unist-util-is by providing a way to retrieve nodes based on complex queries, whereas unist-util-is is more focused on testing nodes against specified conditions.

README

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 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

• 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

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