Consider removing expose(), call() and kill() ?

	worker.expose = methodName => {
		worker[i] = function() {
			return worker.call(methodName, [].slice.call(arguments));
		};
	};

Instead methodName parameter should be used:

	worker.expose = methodName => {
		worker[methodName] = function() {
			return worker.call(methodName, [].slice.call(arguments));
		};
	};

Beside that I don't see why the call and expose methods are accessible from outside. (Don't assign to worker at all) The purpose of the kill method is also not clear for me.