The isScript() method of the TrustedTypePolicyFactory interface returns true if it is passed a valid TrustedScript object.

value

A TrustedScript object.

A boolean that is true if the object is a valid TrustedScript object.

In the below example the constant url was created by a policy, and therefore isScriptURL() returns true. The second example is an attempt to fake an object, and the third is a string. Both of these will return false when passed to isScriptURL().

const myScript = policy.createScript("eval('2 + 2')");
console.log(trustedTypes.isScript(myScript)); // true;

const fake = Object.create(TrustedScript.prototype);
console.log(trustedTypes.isScript(fake)); // false

console.log(trustedTypes.isScript("eval('2 + 2')")); // false