JS Html Sanitizer

Very fast client-side HTML Sanitizer (front-end only, i.e. "needs a browser", won't work in Node) to prevent XSS and unwanted tags in UGC.

Please note: to prevent XSS attacks you should always sanitize input on the server too. Never trust the client!

Usage:

<script src="https://cdn.jsdelivr.net/gh/jitbit/HtmlSanitizer@master/HtmlSanitizer.js"></script>
<!-- or simply install locally: <script src="HtmlSanitizer.js"></script> -->

<script>
    var html = HtmlSanitizer.SanitizeHtml("<div> <script> Alert('xss!'); </sc" + "ript> </div>");
    //html == "<div>  </div>";
</script>

The sanitizer uses whitelisting approach (as opposed to "blacklisting") to clean out everything that's not allowed.

Speed

It uses browser/DOM to parse the html by creating an invisible "sandboxed" iframe (hence the browser "front-end only" requirement) which makes it much faster than "pure JavaScript" sanitizers.

Tested on https://www.bbc.co.uk homepage - the page is sanitized ~370 times per second on an i5 core CPU in Firefox Quantum (tested via benchmark.js)

Tags allowed by default

a, abbr, b, blockquote, body, br, center, code, div, em, font, h1, h2, h3, h4, h5, h6, hr, i, img, label, li, ol, p, pre, small, source, span, strong, table, tbody, tr, td, th, thead, ul, u, video

Attributes allowed by default

align, color, controls, height, href, src, style, target, title, type, width

CSS styles allowed by default

color, background-color, font-size, text-align, text-decoration, font-weight

Schemas allowed by default

http:, https:, data:

(allowed in 'src', 'href' and similar "uri-attributes". To clean up stuff like <a href='javascript:alert()'></a>)

Configuring

Allowed tags, attributes and styles are listed in AllowedTags, AllowedAttributes and AllowedCssStyles public properties. To disallow a tag remove it from the dictionary like this:

delete HtmlSanitizer.AllowedTags['table']

To add an allowed tag:

HtmlSanitizer.AllowedTags['script'] = true;

Browser support

Supported by all major browsers, IE10 and higher.

BUT WHY?

Why create a front-end HTML sanitizer if the input has to be sanitized on the server anyway?

Users often copy-paste awful HTML generated by MS Word, MS Outlook or Apple Mail that needs a clean-up. Or you need to remove excessive formatting in an WYSIWYG editor. Or you need to display an (ugly) email message in a (beatuful) mobile app. Or (my favorite) you simply need to ease the load in the server-side sanitizer. And many many other use-cases.

JavascriptReallyWorks / HtmlSanitizer