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AMP Purifier

src/purifier/README.md

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AMP Purifier

The AMP Purifier library contains an AMP-specific configuration for DOMPurify.

This library is internally used by amp-mustache to sanitize rendered Mustache.js templates before displaying them.

Usage

js
import {Purifier} from '#purifier';

const purifier = new Purifier(document);
purifier.purifyHtml('a<script>b</script>c'); // "ac"

Usage with Mustache.js

js
import Mustache from 'mustache';
import {Purifier} from '#purifier';

const purifier = new Purifier(document);
const _unescapedValue = Mustache.Writer.prototype.unescapedValue;
Mustache.Writer.prototype.unescapedValue = function (token, context) {
  const result = _unescapedValue(token, context);
  return purifier.purifyTagsForTripleMustache(result);
};
const html = Mustache.render(template, data);

const body = purifier.purifyHtml(html);
for (const child of body.children) {
  targetElement.appendChild(child);
}

Reference

The library has only a single export, the Purifier class.

Purifier constructor

new Purifier(doc, config, attrRewrite)

doc

The base document to use. Usually window.document.

config

Optional

DOMPurify configuration to use in addition to the AMP default one.

attrRewrite

Optional

A function that, if provided, will be called for every sanitized attribute in the output to change its value. It accepts the following attributes:

  • tagName - name of tag containing the attribute
  • attrName - name of attribute
  • attrValue - current attribute value

The returned value of this function is used as the new attribute value.

For example, this replaces the href of all <a> elements with example.com:

js
new Purifier(window.document, {}, (tagName, attrName, attrValue) => {
  if (tagName === 'a' && attrName === 'href') {
    return 'https://google.com';
  }
  return attrValue;
});

purifyHtml

purifyHtml(html)

Uses DOMPurify to sanitize HTML in a way that ensures the fragment is valid AMP.

html

The HTML code to sanitize (purify).

Return value

A <body> element containing the sanitized html markup.

purifyTagsForTripleMustache

purifyTagsForTripleMustache(html)

Uses DOMPurify to sanitize HTML with stricter policy for unescaped templates e.g. triple mustache. See amp-mustache documentation for more information.

html

The HTML code to sanitize (purify).

Return value

Sanitized HTML (as a string).

getAllowedTags

getAllowedTags()

Gets a copy of the map of allowed tag names (standard DOMPurify config).

Return value

An object containing the list of allowed tags according to AMP's DOMPurify config.

validateAttributeChange

Returns whether an attribute addition/modification/removal is valid according to AMP's DOMPurify config.

validateAttributeChange(node, attr, value)

node

DOM node to check.

attr

Attribute name.

value

Attribute value (can be null).

Return value

true if the given attribute change is valid, false otherwise.