The Tor Browser / file revision

 // Test extracting frame.arguments element getters and calling them in

 // various awkward ways.

 load(libdir + "asserts.js");

 var g = newGlobal();

 var dbg = Debugger(g);

 var hits = 0;

 var fframe, farguments, fgetter;

 dbg.onDebuggerStatement = function (frame) {

     if (hits === 0) {

         fframe = frame;

         farguments = frame.arguments;

         fgetter = Object.getOwnPropertyDescriptor(farguments, "0").get;

         assertEq(fgetter instanceof Function, true);

         // Calling the getter without an appropriate this-object

         // fails, but shouldn't assert or crash.

         assertThrowsInstanceOf(function () { fgetter.call(Math); }, TypeError);

     } else {

         // Since fframe is still on the stack, fgetter can be applied to it.

         assertEq(fframe.live, true);

         assertEq(fgetter.call(farguments), 100);

         // Since h was called without arguments, there is no argument 0.

         assertEq(fgetter.call(frame.arguments), undefined);

     }

     hits++;

 };

 g.eval("function h() { debugger; }");

 g.eval("function f(x) { debugger; h(); }");

 g.f(100);

 assertEq(hits, 2);

 // Now that fframe is no longer live, trying to get its arguments should throw.

 assertEq(fframe.live, false);

 assertThrowsInstanceOf(function () { fgetter.call(farguments); }, Error);