Often times you have a function that takes a certain set of arguments. Like the following adder function:

var adder = function(a,b,c) {
  return a + b + c;
};

But you are left trying to pass in arguments as an array (e.g. [1,2,3]). You want to be able to splat the array of arguments so that it matches the function declaration. This can be done by using apply.

> adder.apply(undefined, [1,2,3])
6