The Tor Browser / file revision

 var g = newGlobal();

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

 var dbg = new Debugger;

 var gw = dbg.addDebuggee(g);

 var fw = gw.getOwnPropertyDescriptor("f").value;

 assertEq(fw.parameterNames.toString(), "x");

 var g = newGlobal();

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

 var dbg = Debugger(g);

 dbg.onDebuggerStatement = function (frame) {

     var result = frame.eval("arguments");

     assertEq("throw" in result, true);

     var result2 = frame.evalWithBindings("exc instanceof SyntaxError", {exc: result.throw});

     assertEq(result2.return, true);

 };

 g.f();