The defaultPolicy read-only property of the TrustedTypePolicyFactory interface returns the default TrustedTypePolicy or null if this is empty.

A TrustedTypePolicy or null.

The first line below returns null as no default policy has been created. Once a default policy is created, calling defaultPolicy returns that policy object.

console.log(trustedTypes.defaultPolicy); // null
const dp = trustedTypes.createPolicy("default", {});
console.log(trustedTypes.defaultPolicy); // a TrustedTypePolicy object