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https://github.com/syntax-tree/hast-util-assert

utility to assert hast nodes
https://github.com/syntax-tree/hast-util-assert

assert hast hast-util html unist util

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utility to assert hast nodes

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# hast-util-assert



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[![Downloads][downloads-badge]][downloads]

[![Size][size-badge]][size]

[![Sponsors][sponsors-badge]][collective]

[![Backers][backers-badge]][collective]

[![Chat][chat-badge]][chat]



[hast][] utility to assert trees.



## Contents



*   [What is this?](#what-is-this)

*   [When should I use this?](#when-should-i-use-this)

*   [Install](#install)

*   [Use](#use)

*   [API](#api)

    *   [`assert(tree[, parent])`](#asserttree-parent)

    *   [`parent(tree[, parent])`](#parenttree-parent)

    *   [`literal(node[, parent])`](#literalnode-parent)

    *   [`_void(node[, parent])`](#_voidnode-parent)

    *   [`wrap(fn)`](#wrapfn)

    *   [`AssertionError`](#assertionerror)

*   [Types](#types)

*   [Compatibility](#compatibility)

*   [Security](#security)

*   [Related](#related)

*   [Contribute](#contribute)

*   [License](#license)



## What is this?



This package is a tiny utility that helps you deal with nodes.



## When should I use this?



This utility is typically useful when you expect certain nodes in your APIs

and want to make sure they’re valid and as expected.



A different utility, [`unist-util-assert`][unist-util-assert], does the same but

for any [unist][] node.



## Install



This package is [ESM only][esm].

In Node.js (version 16+), install with [npm][]:



```sh

npm install hast-util-assert

```



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



```js

import {assert} from 'https://esm.sh/hast-util-assert@4'

```



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



```html



  import {assert} from 'https://esm.sh/hast-util-assert@4?bundle'



```



## Use



```js

import {assert} from 'hast-util-assert'



assert({type: 'root', children: []})

assert({type: 'element', tagName: 'a', properties: {}, children: []})

// All OK.



assert({children: []})

// AssertionError: node should have a type: `{ children: [] }`



assert({type: 'element', properties: {}, children: []})

// AssertionError: `element` should have a `tagName`: `{ type: 'element', properties: {}, children: [] }`

```



## API



This package exports the identifiers [`_void`][api-void],

[`assert`][api-assert],

[`literal`][api-literal],

[`parent`][api-parent], and

[`wrap`][api-wrap].

There is no default export.



### `assert(tree[, parent])`



Assert that `tree` is a valid hast [`Node`][node].



If `tree` is a parent, all children will be asserted too.



Supports unknown hast nodes.



###### Parameters



*   `tree` (`unknown`)

    — thing to assert

*   `parent` ([`Parent`][parent-node], optional)

    — optional, valid parent



###### Returns



Nothing.



###### Throws



When `tree` (or its descendants) is not a hast node

([`AssertionError`][api-assertion-error]).



### `parent(tree[, parent])`



Assert that `tree` is a valid hast [`Parent`][parent-node].



All children will be asserted too.



Supports unknown hast nodes.



###### Parameters



*   `tree` (`unknown`)

    — thing to assert

*   `parent` ([`Parent`][parent-node], optional)

    — optional, valid parent



###### Returns



Nothing.



###### Throws



When `tree` is not a parent or its descendants are not nodes

([`AssertionError`][api-assertion-error])



### `literal(node[, parent])`



Assert that `node` is a valid hast [`Literal`][literal-node].



Supports unknown hast nodes.



###### Parameters



*   `node` (`unknown`)

    — thing to assert

*   `parent` ([`Parent`][parent-node], optional)

    — optional, valid parent



###### Returns



Nothing.



###### Throws



When `node` is not a hast literal ([`AssertionError`][api-assertion-error]).



### `_void(node[, parent])`



Re-exported from [`unist-util-assert`][unist-util-assert-void].



### `wrap(fn)`



Re-exported from [`unist-util-assert`][unist-util-assert-wrap].



### `AssertionError`



Re-exported from [`unist-util-assert`][unist-util-assert-assertion-error].



## Types



This package is fully typed with [TypeScript][].

It exports the additional type [`AssertionError`][api-assertion-error].



## 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-assert@^4`,

compatible with Node.js 16.



## Security



`hast-util-assert` does not change the syntax tree so there are no openings for

[cross-site scripting (XSS)][xss] attacks.



## Related



*   [`unist-util-assert`][unist-util-assert]

    — check [unist](https://github.com/syntax-tree/unist) nodes

*   [`mdast-util-assert`](https://github.com/syntax-tree/mdast-util-assert)

    — check [mdast](https://github.com/syntax-tree/mdast) nodes

*   [`nlcst-test`](https://github.com/syntax-tree/nlcst-test)

    — check [nlcst](https://github.com/syntax-tree/nlcst) nodes



## 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]



[build-badge]: https://github.com/syntax-tree/hast-util-assert/workflows/main/badge.svg



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



[coverage-badge]: https://img.shields.io/codecov/c/github/syntax-tree/hast-util-assert.svg



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



[downloads-badge]: https://img.shields.io/npm/dm/hast-util-assert.svg



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



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



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



[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



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



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



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



[parent-node]: https://github.com/syntax-tree/unist#parent-1



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



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



[xss]: https://en.wikipedia.org/wiki/Cross-site_scripting



[unist-util-assert-void]: https://github.com/syntax-tree/unist-util-assert#_voidnode-parent



[unist-util-assert-wrap]: https://github.com/syntax-tree/unist-util-assert#wrapfn



[unist-util-assert-assertion-error]: https://github.com/syntax-tree/unist-util-assert#assertionerror



[api-void]: #_voidnode-parent



[api-assert]: #asserttree-parent



[api-literal]: #literalnode-parent



[api-parent]: #parenttree-parent



[api-wrap]: #wrapfn



[api-assertion-error]: #assertionerror