let g = newGlobal(); g.eval('function indirection() { debugger; }'); g.eval('function* f() { print(uneval(indirection())); }'); let dbg = new Debugger(g); dbg.onDebuggerStatement = frame => { frame = frame.older; // drill down to f's frame return frame.eval("arguments"); // this fails }; g.f(1, 2, 3).next(); ---- More generator-debugging weirdness. This throws an Error with the message "Debugger env is not live". https://searchfox.org/mozilla-central/source/js/src/vm/EnvironmentObject.cpp#2038 DebugEnvironments::hasLiveEnvironment(env) is returning nullptr. I'm not sure why we can't have a live environment for a resumed generator frame.