The Tor Browser / file revision

 // Test that you can't call the SavedFrame constructor and can only use

 // SavedFrame's getters on SavedFrame instances.

 load(libdir + "asserts.js");

 let proto = Object.getPrototypeOf(saveStack());

 // Can't create new SavedFrame instances by hand.

 assertThrowsInstanceOf(() => {

   new proto.constructor();

 }, TypeError);

 for (let p of ["source", "line", "column", "functionDisplayName", "parent"]) {

   // The getters shouldn't work on the prototype.

   assertThrowsInstanceOf(() => proto[p], TypeError);

   // Nor should they work on random objects.

   let o = {};

   Object.defineProperty(o, p, Object.getOwnPropertyDescriptor(proto, p));

   assertThrowsInstanceOf(() => o[p], TypeError);

 }