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

value

A TrustedHTML object.

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

In the below example the constant html was created by a policy, and therefore isHTML() 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 isHTML().

const html = policy.createHTML("<div>");
console.log(trustedTypes.isHTML(html)); // true;

const fake = Object.create(TrustedHTML.prototype);
console.log(trustedTypes.isHTML(fake)); // false

console.log(trustedTypes.isHTML("<div>plain string</div>")); // false