Consider adding TT.emptyScript

[koto]

This might be used to check for the eval(TrustedScript) support. It can't be polyfilled, and requires some support from the JavaScript runtime, so it's possible there would exist environments in which eval(TrustedScript) is not available, whereas other TT restrictions are supported. The check then might be:

if (eval(trustedTypes.emptyScript)) {
  // Traditionally, eval(nonString) returns its input, and Objects are truthy.
  eval("we_have_to_use_strings_here");
} else { 
  // eval(TrustedScript) would execute if supported, returning a falsy value.
  eval(myTrustedScriptObj)
}

or

eval(memoize(eval(trustedTypes.emptyString)) ? trustedScript.toString() : trustedScript)

That would allow authors to set up script-src 'unsafe-eval' 'trusted-script'; trusted-types a b c which would lock down eval() as much as it is possible for a given environment.