hast-util-truncate/readme.md

hast utility to truncate the tree to a certain number of characters

# hast-util-truncate

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[hast][] utility to truncate the tree to a certain number of characters.

## Contents

*   [What is this?](#what-is-this)
*   [When should I use this?](#when-should-i-use-this)
*   [Install](#install)
*   [Use](#use)
*   [API](#api)
    *   [`truncate(tree[, options])`](#truncatetree-options)
    *   [`Options`](#options)
*   [Types](#types)
*   [Compatibility](#compatibility)
*   [Security](#security)
*   [Related](#related)
*   [Contribute](#contribute)
*   [License](#license)

## What is this?

This package is a utility that takes a [hast][] (HTML) syntax tree and truncates
it to a certain number of characters, while otherwise preserving the tree
structure.

## When should I use this?

This is a small utility useful when you need to create a shorter version of a
potentially long document.

This utility is similar to [`hast-util-excerpt`][hast-util-excerpt], which
truncates a tree to a certain comment.

The rehype plugin
[`rehype-infer-description-meta`][rehype-infer-description-meta]
wraps both this utility and `hast-util-excerpt` to figure out a description of a
document, for use with [`rehype-meta`][rehype-meta].

## Install

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

```sh
npm install hast-util-truncate
```

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

```js
import {truncate} from 'https://esm.sh/hast-util-truncate@2'
```

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

```html
<script type="module">
  import {truncate} from 'https://esm.sh/hast-util-truncate@2?bundle'
</script>
```

## Use

Say our module `example.js` looks as follows:

```js
import {h} from 'hastscript'
import {truncate} from 'hast-util-truncate'

const tree = h('p', [
  'Lorem ipsum dolor sit amet, ',
  h('em', 'consectetur'),
  'adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud'
])

console.log(truncate(tree, {ellipsis: '…'}));
```

…now running `node example.js` yields:

```js
{
  type: 'element',
  tagName: 'p',
  properties: {},
  children: [
    {type: 'text', value: 'Lorem ipsum dolor sit amet, '},
    {
      type: 'element',
      tagName: 'em',
      properties: {},
      children: [{type: 'text', value: 'consectetur'}]
    },
    {
      type: 'text',
      value: 'adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim…'
    }
  ]
}
```

## API

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

### `truncate(tree[, options])`

Truncate the tree to a certain number of characters.

###### Parameters

*   `tree` ([`Node`][node])
    — tree to truncate
*   `options` ([`Options`][api-options], optional)
    — configuration

###### Returns

Truncated copy of `tree` ([`Node`][node]).

### `Options`

Configuration (TypeScript type).

##### Fields

###### `options.size`

Number of characters to truncate to (`number`, default: `140`).

###### `options.ellipsis`

Value to use at truncation point (`string`, optional).

###### `options.maxCharacterStrip`

How far to walk back (`number`, default: `30`).
The algorithm attempts to break right after a word rather than the exact `size`.
Take for example the `|`, which is the actual break defined by `size`, and the
`…` is the location where the ellipsis is placed: `This… an|d that`.
Breaking at `|` would at best look bad but could likely result in things such as
`ass…` for `assignment`, which is not ideal.
`maxCharacterStrip` defines how far back the algorithm will walk to find a
pretty word break.
This prevents a potential slow operation on larger `size`s without any
whitespace.
If `maxCharacterStrip` characters are walked back and no nice break point is
found, the bad break point is used.
Set `maxCharacterStrip: 0` to not find a nice break.

###### `options.ignore`

Nodes to exclude from the resulting tree (`Array<Node>`).
These are not counted towards `size`.

## Types

This package is fully typed with [TypeScript][].
It exports the additional type [`Options`][api-options].

## 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, `hast-util-truncate@^2`,
compatible with Node.js 16.

## Security

Use of `hast-util-truncate` should be safe if the tree is already safe and
you’re not using user content in options.
When in doubt, use [`hast-util-sanitize`][hast-util-sanitize].

## Related

*   [`hast-util-excerpt`][hast-util-excerpt]
    — truncate the tree to a comment
*   [`rehype-infer-description-meta`][rehype-infer-description-meta]
    — infer file metadata from the contents of the document
*   [`rehype-meta`][rehype-meta]
    — add metadata to the head of a document

## 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/hast-util-truncate/workflows/main/badge.svg

[build]: https://github.com/syntax-tree/hast-util-truncate/actions

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[coverage]: https://codecov.io/github/syntax-tree/hast-util-truncate

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[downloads]: https://www.npmjs.com/package/hast-util-truncate

[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=hast-util-truncate

[size]: https://bundlejs.com/?q=hast-util-truncate

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

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

[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

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

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

[hast-util-sanitize]: https://github.com/syntax-tree/hast-util-sanitize

[hast-util-excerpt]: https://github.com/syntax-tree/hast-util-excerpt

[rehype-infer-description-meta]: https://github.com/rehypejs/rehype-infer-description-meta

[rehype-meta]: https://github.com/rehypejs/rehype-meta

[api-truncate]: #truncatetree-options

[api-options]: #options