IIFE and Global scope in javascript

Question

Why does the following code result in logging of b while a is still undefined?

(function(){ var a=b=5; })();
console.log('b:'+b);
console.log('a:'+a);

Answer 1

Because var a=b=5; statement defines only local a variable and in fact is interpreted like

var a = (b=5);

which equals to

b = 5;
var a = 5;

which assigns 5 to a global b variable and defines a local a variable.

The proper way to define 2 local variables without value repetition would be

var b = 5, a = b;