Javascript: var = var = function

Quentin did a very good job telling you what it is doing. I just wanted to chime in to give an example where you might use this:

Say for instance you have an object:

var obj = {
    init: function() {
        var x = this.x = [1,2,3];
    }
};

What this allows you to do is reference your x variable two different ways (either through x or this.x).

Now why would you do this? Well two major reasons.

1. It is faster to access x rather than this.x (but you still need to access it elsewhere)
2. It produces easier to read code when having to read/write to x lots of times in one function.

This is just another reason why you would use it.

But in most cases it is just aliases, such as: forEach -> each

Here's an explanation using operator associativity and precedence.

So, looking at an operator precedence description from Mozilla, when an expression includes multiple operators of the same precedence, as in

a OP b OP c

, then you check whether that level of precedence uses right-to-left or left-to-right associativity.

a = b = c

The assignment operator in JavaScript is the only operator on its level of precedence.

It has right-to-left associativity

So in a = b = c, b = c is evaluated first, assigning the value of c to b.

Then the expression becomes a = b.