# unist-util-modify-children

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[unist][] utility to change children of a parent.

## Contents

*   [What is this?](#what-is-this)
*   [When should I use this?](#when-should-i-use-this)
*   [Install](#install)
*   [Use](#use)
*   [API](#api)
    *   [`modifyChildren(modifier)`](#modifychildrenmodifier)
    *   [`Modifier`](#modifier)
    *   [`Modify`](#modify)
*   [Types](#types)
*   [Compatibility](#compatibility)
*   [Related](#related)
*   [Contribute](#contribute)
*   [License](#license)

## What is this?

This is a tiny utility that you can use to create a reusable function that
modifies children.

## When should I use this?

Probably never!
Use [`unist-util-visit`][unist-util-visit].

## Install

This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:

```sh
npm install unist-util-modify-children
```

In Deno with [`esm.sh`][esmsh]:

```js
import {modifyChildren} from 'https://esm.sh/unist-util-modify-children@4'
```

In browsers with [`esm.sh`][esmsh]:

```html
<script type="module">
  import {modifyChildren} from 'https://esm.sh/unist-util-modify-children@4?bundle'
</script>
```

## Use

```js
import u from 'unist-builder'
import {modifyChildren} from 'unist-util-modify-children'

const tree = u('root', [
  u('leaf', '1'),
  u('parent', [u('leaf', '2')]),
  u('leaf', '3')
])
const modify = modifyChildren(function (node, index, parent) {
  if (node.type === 'parent') {
    parent.children.splice(index, 1, {type: 'subtree', children: parent.children})
    return index + 1
  }
})

modify(tree)

console.dir(tree, {depth: undefined})
```

Yields:

```js
{
  type: 'root',
  children: [
    {type: 'leaf', value: '1'},
    {type: 'subtree', children: [{type: 'leaf', value: '2'}]},
    {type: 'leaf', value: '3'}
  ]
}
```

## API

This package exports the identifier [`modifyChildren`][api-modifychildren].
There is no default export.

### `modifyChildren(modifier)`

Wrap `modifier` to be called for each child in the nodes later given to
`modify`.

###### Parameters

*   `modifier` ([`Modifier`][api-modifier])
    — callback called for each `child` in `parent` later given to `modify`

###### Returns

Modify children of `parent` ([`Modify`][api-modify]).

### `Modifier`

Callback called for each `child` in `parent` later given to `modify`
(TypeScript type).

###### Parameters

*   `child` ([`Node`][node])
    — child of `parent`
*   `index` (`number`)
    — position of `child` in `parent`
*   `parent` ([`Node`][node])
    — parent node

###### Returns

Position to move to next (optional) (`number` or `undefined`).

### `Modify`

Modify children of `parent` (TypeScript type).

###### Parameters

*   `parent` ([`Node`][node])
    — parent node

###### Returns

Nothing (`undefined`).

## Types

This package is fully typed with [TypeScript][].
It exports the additional types [`Modifier`][api-modifier] and
[`Modify`][api-modify].

## 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-modify-children@^4`, compatible with Node.js 16.

## Related

*   [`unist-util-visit`](https://github.com/syntax-tree/unist-util-visit)
    — walk the tree
*   [`unist-util-visit-parents`](https://github.com/syntax-tree/unist-util-visit-parents)
    — walk the tree with a stack of parents
*   [`unist-util-filter`](https://github.com/syntax-tree/unist-util-filter)
    — create a new tree with all nodes that pass a test
*   [`unist-util-map`](https://github.com/syntax-tree/unist-util-map)
    — create a new tree with all nodes mapped by a given function
*   [`unist-util-flatmap`](https://gitlab.com/staltz/unist-util-flatmap)
    — create a new tree by mapping (to an array) with the given function
*   [`unist-util-find-after`](https://github.com/syntax-tree/unist-util-find-after)
    — find a node after another node
*   [`unist-util-find-before`](https://github.com/syntax-tree/unist-util-find-before)
    — find a node before another node
*   [`unist-util-find-all-after`](https://github.com/syntax-tree/unist-util-find-all-after)
    — find all nodes after another node
*   [`unist-util-find-all-before`](https://github.com/syntax-tree/unist-util-find-all-before)
    — find all nodes before another node
*   [`unist-util-find-all-between`](https://github.com/mrzmmr/unist-util-find-all-between)
    — find all nodes between two nodes
*   [`unist-util-remove`](https://github.com/syntax-tree/unist-util-remove)
    — remove nodes from a tree that pass a test
*   [`unist-util-select`](https://github.com/syntax-tree/unist-util-select)
    — select nodes with CSS-like selectors

## Contribute

See [`contributing.md`][contributing] in [`syntax-tree/.github`][health] for
ways to get started.
See [`support.md`][support] for ways to get help.

This project has a [code of conduct][coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.

## License

[MIT][license] © [Titus Wormer][author]

<!-- Definitions -->

[build-badge]: https://github.com/syntax-tree/unist-util-modify-children/workflows/main/badge.svg

[build]: https://github.com/syntax-tree/unist-util-modify-children/actions

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[coverage]: https://codecov.io/github/syntax-tree/unist-util-modify-children

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[downloads]: https://www.npmjs.com/package/unist-util-modify-children

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[size]: https://bundlejs.com/?q=unist-util-modify-children

[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg

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[collective]: https://opencollective.com/unified

[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg

[chat]: https://github.com/syntax-tree/unist/discussions

[npm]: https://docs.npmjs.com/cli/install

[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[esmsh]: https://esm.sh

[typescript]: https://www.typescriptlang.org

[license]: license

[author]: https://wooorm.com

[health]: https://github.com/syntax-tree/.github

[contributing]: https://github.com/syntax-tree/.github/blob/main/contributing.md

[support]: https://github.com/syntax-tree/.github/blob/main/support.md

[coc]: https://github.com/syntax-tree/.github/blob/main/code-of-conduct.md

[unist]: https://github.com/syntax-tree/unist

[node]: https://github.com/syntax-tree/unist#nodes

[unist-util-visit]: https://github.com/syntax-tree/unist-util-visit

[api-modifychildren]: #modifychildrenmodifier

[api-modifier]: #modifier

[api-modify]: #modify