The HTML Sanitizer API is a browser-native API that safely sanitizes untrusted HTML strings, removing potentially dangerous content such as <script> tags, inline event handlers (onclick, onerror, etc.), and javascript: URLs. It is built directly into modern browsers, eliminating the need for third-party libraries like DOMPurify in many use cases. The API is designed to prevent Cross-Site Scripting (XSS) attacks by default, using a secure allowlist-based approach.

Using element.innerHTML = untrustedHTML is dangerous because it executes any embedded JavaScript immediately. The Sanitizer API, when used via element.setHTML(untrustedHTML, { sanitizer }), first strips all executable code and dangerous markup before inserting the HTML into the DOM. This provides a secure alternative without manual escaping or regex-based filtering.

As of 2024, the Sanitizer API is supported in Google Chrome 105+, Microsoft Edge 105+, and other Chromium-based browsers. Firefox and Safari are actively working on implementation. You can check the latest support status on Can I Use. For unsupported browsers, consider using a polyfill or a library like DOMPurify as a fallback.

By default, the Sanitizer API's default configuration removes: <script> and <style> elements, all inline event handler attributes (onclick, onerror, onload, onmouseover, etc.), javascript: URLs in href/src attributes, <iframe>, <object>, <embed>, <form> elements, data: URLs that could execute code, and various other potentially dangerous constructs. It operates on a secure allowlist model where only known-safe elements and attributes pass through.

Yes! You can create a Sanitizer instance with a custom configuration object. For example: new Sanitizer({ allowElements: ['div', 'p', 'a'], allowAttributes: { 'a': ['href'] } }). This gives you fine-grained control over which elements and attributes are permitted while still blocking everything dangerous by default. Use the Custom preset above to experiment with different configurations.

The Sanitizer API provides strong, browser-level protection against XSS attacks and is maintained by browser vendors with security expertise. However, no sanitizer is 100% guaranteed against all possible attack vectors. The API follows a strict allowlist approach and is regularly updated as new threats emerge. For critical applications, always follow defense-in-depth practices: sanitize input, use Content Security Policy (CSP) headers, and keep your browser updated.

First, check for browser support: if ('Sanitizer' in window) { ... }. Then create a sanitizer instance with your desired configuration and use element.setHTML(untrustedHTML, { sanitizer: mySanitizer }) to safely insert content. Always provide a fallback (like DOMPurify) for browsers that don't yet support the API. Monitor the MDN documentation for the latest API changes and browser support updates.

The most popular alternative is DOMPurify, a fast, battle-tested JavaScript library that works across all browsers. Other options include sanitize-html (Node.js/Browser), Google Caja, and server-side sanitization libraries. The Sanitizer API's main advantage is that it's built into the browser, requires no additional downloads, and benefits from native performance and automatic security updates.

Yes. The Sanitizer API includes protections against DOM clobbering attacks, where an attacker injects HTML elements with id or name attributes that conflict with existing JavaScript variables or DOM properties. The API's default configuration carefully handles these cases, and its design follows secure-by-default principles that mitigate this class of vulnerability.

Mutation XSS (mXSS) is a sophisticated attack where seemingly safe HTML mutates into dangerous code when parsed by the browser. The Sanitizer API is specifically designed to prevent mXSS by using the browser's own parsing engine consistently and applying sanitization at the correct stage. This eliminates the parsing mismatches that mXSS attacks exploit, providing stronger protection than many JavaScript-based sanitizers.