Javascript: Declaring a variable twice in the same line -- what does it mean (eg. Var x = this.time = this.time || this.time(); )

Question

I recently found the following code, but I have never seen JS like this before. What does it mean, and does it work?

Var x = this.time = this.time || Data.now(); 

Answer 1

This code is a short form of,

this.time = this.time || Data.now();
Var x = this.time; 

But you have to be careful while using this way of coding in other aspects like,

var a = b = 10;

Because here in the above case b will become a global variable.