Multiple left-hand assignment with JavaScript

Question

var var1 = 1,
    var2 = 1,
    var3 = 1;

This is equivalent to this:

var var1 = var2 = var3 = 1;

I'm fairly certain this is the order the variables are defined: var3, var2, var1, which would be equivalent to this:

var var3 = 1, var2 = var3, var1 = var2;

Is there any way to confirm this in JavaScript? Using some profiler possibly?

Answer 1

Actually,

var var1 = 1, var2 = 1, var3 = 1;

is not equivalent to:

var var1 = var2 = var3 = 1;

The difference is in scoping:

function good() {
  var var1 = 1, var2 = 1, var3 = 1;
}

function bad() {
  var var1 = var2 = var3 = 1;
}

good();
console.log(window.var2); // undefined

bad();
console.log(window.var2); // 1. Aggh!

Actually this shows that assignment are right associative. The bad example is equivalent to:

var var1 = (window.var2 = (window.var3 = 1));