unist-util-assert

unist utility to assert trees.

What is this?
When should I use this?
Install
Use
API
Extensions
Types
Compatibility
Related
Contribute
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.

Different utilities, mdast-util-assert, hast-util-assert, and nlcst-test, do the same but for mdast, hast, and nlcst nodes, respectively.

Install

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

npm install unist-util-assert

In Deno with esm.sh:

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

In browsers with esm.sh:

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

Use

import {_void, assert, parent} from 'unist-util-assert'

assert({type: 'root', children: []})
assert({type: 'break'})
assert({type: 'element', properties: {}, children: []})
// All OK.

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

parent({type: 'break'})
// AssertionError: parent should have `children`: `{ type: 'break' }`

assert({type: 'element', properties: function() {}})
// AssertionError: non-specced property `properties` should be JSON: `{ type: 'element', properties: [Function] }`

_void({type: 'text', value: 'Alpha'})
// AssertionError: void should not have `value`: `{ type: 'text', value: 'Alpha' }`

assert({type: 'paragraph', children: ['foo']})
// AssertionError: node should be an object: `'foo'` in `{ type: 'paragraph', children: [ 'foo' ] }`

API

This package exports the identifiers _void, assert, literal, parent, and wrap. There is no default export.

`assert(tree[, parent])`

Assert that tree is a valid unist Node.

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

Parameters

tree (unknown) — thing to assert
parent (Parent, optional) — optional, valid parent

Returns

Nothing.

Throws

When tree (or its descendants) is not a node.

`parent(tree[, parent])`

Assert that tree is a valid unist Parent.

All children will be asserted too.

Parameters

tree (unknown) — thing to assert
parent (Parent, optional) — optional, valid parent

Returns

Nothing.

Throws

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

`literal(node[, parent])`

Assert that node is a valid unist Literal.

Parameters

tree (unknown) — thing to assert
parent (Parent, optional) — optional, valid parent

Returns

Nothing.

Throws

When node is not a literal.

`_void(node[, parent])`

Assert that node is a valid void node.

Parameters

tree (unknown) — thing to assert
parent (Parent, optional) — optional, valid parent

Returns

Nothing.

Throws

When node is not a node, a parent, or a literal.

`wrap(fn)`

Wrapper that adds the current node (and parent, if available) to error messages.

Parameters

fn ((node?: any, parent?: Parent | null | undefined) => asserts node is Node)) — custom assertion

Returns

Wrapped fn.

`AssertionError`

Assertion error from node:assert (TypeScript type).

Type

type AssertionError = import('node:assert').AssertionError

Extensions

This module can be used as a base to test subsets of unist (for an example, see mdast-util-assert). All functions that are exposed from such a module, and functions used internally to test children, should be wrapped in wrap, which adds an inspectable string of the respective node, and its parent when available, to the exposed error message.

Types

This package is fully typed with TypeScript. It exports the additional type AssertionError.

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-assert@^4, compatible with Node.js 16.

mdast-util-assert — assert mdast nodes
hast-util-assert — assert hast nodes
nlcst-test — assert nlcst nodes

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.