How to unshift or add to the beginning of argument

问题:

I've just learned the convention for popping off the first element of the arguments array (which I also learned is actually an Object). Now I need to do the opposite. I need to use an unshift operation to add a value to the beginning of the arguments array (or Object acting like an array). Is this possible? I tried:

Array.prototype.unshift.apply('hello', arguments);

That had no effect on arguments whatsoever.

回答1:

1. use .call() instead of .apply() to invoke unshift()

2. set arguments as the this value of unshift()

3. set 'hello' as the argument to unshift()

---

Array.prototype.unshift.call(arguments, 'hello');

---

As @lonesomeday pointed out, you can use .apply() instead of .call(), but you need to pass an array-like argument as the second argument. So in your case, you'd need to wrap 'hello' in an Array.