Project: syntax-tree/hast-util-sanitize

Package: hast-util-sanitize@4.0.0

  1. Dependents: 0
  2. hast utility to sanitize nodes
  1. util 136
  2. utility 132
  3. unist 128
  4. html 118
  5. hast 72
  6. hast-util 47
  7. clean 6
  8. xss 2
  9. sanitize 2


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hast utility to make trees safe.


What is this?

This package is a utility that can make a tree that potentially contains dangerous user content safe for use. It defaults to what GitHub does to clean unsafe markup, but you can change that.

When should I use this?

This package is needed whenever you deal with potentially dangerous user content.

The plugin rehype-sanitize wraps this utility to also sanitize HTML at a higher-level (easier) abstraction.


This package is ESM only. In Node.js (version 12.20+, 14.14+, 16.0+, or 18.0+), install with npm:

npm install hast-util-sanitize

In Deno with esm.sh:

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

In browsers with esm.sh:

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


import {u} from 'unist-builder'
import {h} from 'hastscript'
import {sanitize} from 'hast-util-sanitize'
import {toHtml} from 'hast-util-to-html'

const tree = h('div', {onmouseover: 'alert("alpha")'}, [
    {href: 'jAva script:alert("bravo")', onclick: 'alert("charlie")'},
  u('text', '\n'),
  h('script', 'alert("charlie")'),
  u('text', '\n'),
  h('img', {src: 'x', onerror: 'alert("delta")'}),
  u('text', '\n'),
  h('iframe', {src: 'javascript:alert("echo")'}),
  u('text', '\n'),
  h('math', h('mi', {'xlink:href': 'data:x,<script>alert("foxtrot")</script>'}))

const unsanitized = toHtml(tree)
const sanitized = toHtml(sanitize(tree))



<div onmouseover="alert(&#x22;alpha&#x22;)"><a href="jAva script:alert(&#x22;bravo&#x22;)" onclick="alert(&#x22;charlie&#x22;)">delta</a>
<img src="x" onerror="alert(&#x22;delta&#x22;)">
<iframe src="javascript:alert(&#x22;echo&#x22;)"></iframe>
<math><mi xlink:href="data:x,<script>alert(&#x22;foxtrot&#x22;)</script>"></mi></math></div>



<img src="x">



This package exports the identifiers sanitize and defaultSchema. There is no default export.

sanitize(tree[, schema])

Sanitize a tree.


A new, sanitized, tree (Node).


Sanitation schema that defines if and how nodes and properties should be cleaned. The default schema is exported as defaultSchema, which defaults to GitHub style sanitation. If any top-level key isn’t given, it defaults to GitHub’s style too.

For a thorough sample, see the code for defaultSchema.

To extend the standard schema with a few changes, clone defaultSchema like so:

import {h} from 'hastscript'
import deepmerge from 'deepmerge' // You can use `structuredClone` in modern JS.
import {sanitize, defaultSchema} from 'hast-util-sanitize'

const schema = deepmerge(defaultSchema, {attributes: {'*': ['className']}})

const tree = sanitize(h('div', {className: ['foo']}), schema)

// `tree` still has `className`.
// {
//   type: 'element',
//   tagName: 'div',
//   properties: {className: ['foo']},
//   children: []
// }

Map of tag names to allowed property names (Record<string, Array<string>>).

The special '*' key defines property names allowed on all elements.

One special value, 'data*', can be used to allow all data properties.

attributes: {
  a: ['href'],
  img: ['src', 'longDesc'],
  // …
  '*': [
    // …

Instead of a single string (such as type), which allows any property value of that property name, it’s also possible to provide an array (such as ['type', 'checkbox']), where the first entry is the property name, and all other entries allowed property values. This is how the default GitHub schema allows only disabled checkbox inputs:

attributes: {
  // …
  input: [
    ['type', 'checkbox'],
    ['disabled', true]
  // …

This also plays well with properties that accept space- or comma-separated values, such as class. Say you wanted to allow certain classes on span elements for syntax highlighting, that can be done like this:

// …
span: [
  ['className', 'token', 'number', 'operator']
// …

Map of tag names to required property names and their default property value (Record<string, Record<string, *>>). If the defined keys do not exist in an element’s properties, they are added and set to the specified value.

Note that properties are first checked based on the schema at attributes, so properties could be removed by that step and then added again through required.

required: {
  input: {type: 'checkbox', disabled: true}

List of allowed tag names (Array<string>).

tagNames: [
  // …

Map of protocols to allow in property values (Record<string, Array<string>>).

protocols: {
  href: ['http', 'https', 'mailto'],
  // …
  longDesc: ['http', 'https']

Map of tag names to their required ancestor elements (Record<string, Array<string>>).

ancestors: {
  li: ['ol', 'ul'],
  // …
  tr: ['table']

List of allowed property names which can clobber (Array<string>).

clobber: ['name', 'id']

Prefix to use before potentially clobbering property names (string).

clobberPrefix: 'user-content-'

Names of elements to strip from the tree (Array<string>).

By default, unsafe elements are replaced by their children. Some elements, should however be entirely stripped from the tree.

strip: ['script']

Whether to allow comments (boolean, default: false).

allowComments: true

Whether to allow doctypes (boolean, default: false).

allowDoctypes: true


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


Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. Our projects sometimes work with older versions, but this is not guaranteed.


By default, hast-util-sanitize will make everything safe to use. But when used incorrectly, deviating from the defaults can open you up to a cross-site scripting (XSS) attack.

Use hast-util-sanitize after the last unsafe thing: everything after it could be unsafe (but is fine if you do trust it).


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.


MIT © Titus Wormer