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.

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.

• javascript
• arrays
• arguments
• javascript-objects
• argument-passing

• You cannot modify the arguments collection. You can modify the argument values, but not the length of the collection etc. – Pointy Commented Nov 11, 2013 at 18:51
• @Pointy: Yes, you can modify its length. – Blue Skies Commented Nov 11, 2013 at 18:53
• @BlueSkies yes sorry; what I meant was that you can't mess with it like an array. Changing the length of an array affects array elements after the new length by making them undefined, but updating the length of the arguments object won't do that. I should have worded my comment more clearly. – Pointy Commented Nov 11, 2013 at 18:57

1 Answer 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.