Why apply() here takes only one argument instead of two?

Question

I'm reading the book Javascript: The Good Parts. And I'm confused by the following code.

Function.method('curry', function (  ) {
    var slice = Array.prototype.slice,
        args = slice.apply(arguments),
        that = this;
    return function (  ) {
        return that.apply(null, args.concat(slice.apply(arguments)));
    };
});

Where is the null in slice.apply(arguments)?

Answer 1

arguments is being passed as the context (this), not the function's arguments.

It's equivalent to arguments.slice(), except that arguments.slice() doesn't exist.

Answer 2

That's the equivalent of calling slice() on an array with no arguments - i.e. it returns an array with all the elements of the original array. In this case, 'arguments' is not a true array, so calling Array.prototype.slice on it in effect turns it into one.