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hast utility to create trees with ease.

Contents

What is this?

This package is a hyperscript interface (like createElement from React and h from Vue and such) to help with creating hast trees.

When should I use this?

You can use this utility in your project when you generate hast syntax trees with code. It helps because it replaces most of the repetition otherwise needed in a syntax tree with function calls. It also helps as it improves the attributes you pass by turning them into the form that is required by hast.

You can instead use unist-builder when creating any unist nodes and xastscript when creating xast (XML) nodes.

Install

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

npm install hastscript

In Deno with esm.sh:

import {h} from 'https://esm.sh/hastscript@9'

In browsers with esm.sh:

<script type="module">
  import {h} from 'https://esm.sh/hastscript@9?bundle'
</script>

Use

import {h, s} from 'hastscript'

console.log(
  h('.foo#some-id', [
    h('span', 'some text'),
    h('input', {type: 'text', value: 'foo'}),
    h('a.alpha', {class: 'bravo charlie', download: 'download'}, [
      'delta',
      'echo'
    ])
  ])
)

console.log(
  s('svg', {xmlns: 'http://www.w3.org/2000/svg', viewbox: '0 0 500 500'}, [
    s('title', 'SVG `<circle>` element'),
    s('circle', {cx: 120, cy: 120, r: 100})
  ])
)

Yields:

{
  type: 'element',
  tagName: 'div',
  properties: {className: ['foo'], id: 'some-id'},
  children: [
    {
      type: 'element',
      tagName: 'span',
      properties: {},
      children: [{type: 'text', value: 'some text'}]
    },
    {
      type: 'element',
      tagName: 'input',
      properties: {type: 'text', value: 'foo'},
      children: []
    },
    {
      type: 'element',
      tagName: 'a',
      properties: {className: ['alpha', 'bravo', 'charlie'], download: true},
      children: [{type: 'text', value: 'delta'}, {type: 'text', value: 'echo'}]
    }
  ]
}
{
  type: 'element',
  tagName: 'svg',
  properties: {xmlns: 'http://www.w3.org/2000/svg', viewBox: '0 0 500 500'},
  children: [
    {
      type: 'element',
      tagName: 'title',
      properties: {},
      children: [{type: 'text', value: 'SVG `<circle>` element'}]
    },
    {
      type: 'element',
      tagName: 'circle',
      properties: {cx: 120, cy: 120, r: 100},
      children: []
    }
  ]
}

API

This package exports the identifiers h and s. There is no default export.

The export map supports the automatic JSX runtime. You can pass hastscript or hastscript/svg to your build tool (TypeScript, Babel, SWC) with an importSource option or similar.

h(selector?[, properties][, …children])

Create virtual hast trees for HTML.

Signatures
Parameters
selector

Simple CSS selector (string, optional). Can contain a tag name (foo), IDs (#bar), and classes (.baz). If the selector is a string but there is no tag name in it, h defaults to build a div element, and s to a g element. selector is parsed by hast-util-parse-selector. When string, builds an Element. When nullish, builds a Root instead.

properties

Properties of the element (Properties, optional).

children

Children of the node (Child or Array<Child>, optional).

Returns

Created tree (Result).

Element when a selector is passed, otherwise Root.

s(selector?[, properties][, …children])

Create virtual hast trees for SVG.

Signatures, parameters, and return value are the same as h above. Importantly, the selector and properties parameters are interpreted as SVG.

Child

(Lists of) children (TypeScript type).

When strings or numbers are encountered, they are turned into Text nodes. Root nodes are treated as “fragments”, meaning that their children are used instead.

Type
type Child =
  | Array<Node | number | string | null | undefined>
  | Node
  | number
  | string
  | null
  | undefined

Properties

Map of properties (TypeScript type). Keys should match either the HTML attribute name, or the DOM property name, but are case-insensitive.

Type
type Properties = Record<
  string,
  | boolean
  | number
  | string
  | null
  | undefined
  // For comma- and space-separated values such as `className`:
  | Array<number | string>
  // Accepts value for `style` prop as object.
  | Record<string, number | string>
>

Result

Result from a h (or s) call (TypeScript type).

Type
type Result = Element | Root

Syntax tree

The syntax tree is hast.

JSX

This package can be used with JSX. You should use the automatic JSX runtime set to hastscript or hastscript/svg.

👉 Note: while h supports dots (.) for classes or number signs (#) for IDs in selector, those are not supported in JSX.

🪦 Legacy: you can also use the classic JSX runtime, but this is not recommended. To do so, import h (or s) yourself and define it as the pragma (plus set the fragment to null).

The Use example above can then be written like so, using inline pragmas, so that SVG can be used too:

example-html.jsx:

/** @jsxImportSource hastscript */
console.log(
  <div class="foo" id="some-id">
    <span>some text</span>
    <input type="text" value="foo" />
    <a class="alpha bravo charlie" download>
      deltaecho
    </a>
  </div>
)

example-svg.jsx:

/** @jsxImportSource hastscript/svg */
console.log(
  <svg xmlns="http://www.w3.org/2000/svg" viewbox="0 0 500 500">
    <title>SVG `&lt;circle&gt;` element</title>
    <circle cx={120} cy={120} r={100} />
  </svg>
)

Types

This package is fully typed with TypeScript. It exports the additional types Child, Properties, and Result.

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, hastscript@^9, compatible with Node.js 16.

Security

Use of hastscript can open you up to a cross-site scripting (XSS) when you pass user-provided input to it because values are injected into the syntax tree.

The following example shows how an image is injected that fails loading and therefore runs code in a browser.

const tree = h()

// Somehow someone injected these properties instead of an expected `src` and
// `alt`:
const otherProps = {src: 'x', onError: 'alert(1)'}

tree.children.push(h('img', {src: 'default.png', ...otherProps}))

Yields:

<img src="x" onerror="alert(1)">

The following example shows how code can run in a browser because someone stored an object in a database instead of the expected string.

const tree = h()

// Somehow this isn’t the expected `'wooorm'`.
const username = {
  type: 'element',
  tagName: 'script',
  children: [{type: 'text', value: 'alert(2)'}]
}

tree.children.push(h('span.handle', username))

Yields:

<span class="handle"><script>alert(2)</script></span>

Either do not use user-provided input in hastscript or use hast-util-santize.

Related

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.

License

MIT © Titus Wormer

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