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 a node passes a test.

Install

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

npm:

npm install unist-util-is

Use

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

var node = {type: 'strong'}
var 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

API

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

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

Parameters

• 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

Returns

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

function test(node[, index, parent])

Parameters

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

Context

* — The to is given context.

Returns

boolean? — Whether node matches.

convert(test)

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))

console.log(leafs)

Yields:

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

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