Project: syntax-tree/unist-util-map

Package: unist-util-map@3.1.2

  1. Dependents: 0
  2. unist utility to create a new tree by mapping all nodes
  1. util 136
  2. utility 132
  3. unist 128
  4. tree 31
  5. unist-util 25
  6. node 23
  7. walk 8
  8. visit 6
  9. map 2


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unist utility to create a new tree by mapping all nodes with a given function.


What is this?

This is a small utility that helps you make new trees.

When should I use this?

You can use this utility to create a new tree by mapping all nodes with a given function. Creating new trees like this can lead to performance problems, as it creates new objects for every node. When dealing with potentially large trees, and relatively few changes, use unist-util-visit (or unist-util-visit-parents) instead.

To remove certain nodes, you can also walk the tree with unist-util-visit, or use unist-util-filter (clones the tree instead of mutating) or unist-util-remove (mutates). To create trees, use unist-builder.


This package is ESM only. In Node.js (version 12.20+, 14.14+, 16.0+, 18.0+), install with npm:

npm install unist-util-map

In Deno with esm.sh:

import {map} from "https://esm.sh/unist-util-map@3"

In browsers with esm.sh:

<script type="module">
  import {map} from "https://esm.sh/unist-util-map@3?bundle"


import {u} from 'unist-builder'
import {map} from 'unist-util-map'

const tree = u('tree', [
  u('leaf', 'leaf 1'),
  u('node', [u('leaf', 'leaf 2')]),
  u('leaf', 'leaf 3')

const next = map(tree, (node) => {
  return node.type === 'leaf'
    ? Object.assign({}, node, {value: 'CHANGED'})
    : node

console.dir(next, {depth: null})


  type: 'tree',
  children: [
    {type: 'leaf', value: 'CHANGED'},
    {type: 'node', children: [{type: 'leaf', value: 'CHANGED'}]},
    {type: 'void'},
    {type: 'leaf', value: 'CHANGED'}

👉 Note: next is a changed clone and tree is not mutated.


This package exports the identifier map. There is no default export.

map(tree, mapFunction)

Create a new tree (Node) by mapping all nodes with the given function (MapFunction).


New mapped tree (Node).

function mapFunction(node, index, parent)

Function called with a node (Node), its index (number?), and its parent (Node?) to produce a new node.


Node to be used in the new tree (Node). The children on the returned node are not used. if the original node has children, those are mapped instead.


This package is fully typed with TypeScript. It exports a type MapFunction<Tree extends Node = Node> to properly type MapFunctions.


Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. Our projects sometimes work with older versions, but this is not guaranteed.


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 © azu