Need help for output

Issue

Can anyone answer this?

What will the code below output to the console and why?

(function(){    
  var a = b = 3;    
})();
console.log("a defined? " + (typeof a !== 'undefined'));    
console.log("b defined? " + (typeof b !== 'undefined'));

What will the code below output to the console and why?

var myObject = { 
    foo: "bar",    
    func: function() {    
        var self = this;    
        console.log("outer func:  this.foo = " + this.foo);    
        console.log("outer func:  self.foo = " + self.foo);    
        (function() {    
            console.log("inner func:  this.foo = " + this.foo);   
            console.log("inner func:  self.foo = " + self.foo); 
        }());    
    }    
};    
myObject.func();

Solution

First Code:

(function(){    
  var a = b = 3;    
})();
console.log("a defined? " + (typeof a !== 'undefined'));    
console.log("b defined? " + (typeof b !== 'undefined'));

Output:

a defined? false
b defined? true

Explaination: Here you are using Immediately Invoked function Expression(IIFE). Here a is declared inside function's scope but b is not declared due to which it gets registered to the global scope. Now since you are accessing a and b outside in the global scope a is undefined but b is defined.

Second Code:

var myObject = { 
    foo: "bar",    
    func: function() {    
        var self = this;    
        console.log("outer func:  this.foo = " + this.foo);    
        console.log("outer func:  self.foo = " + self.foo);    
        (function() {    
            console.log("inner func:  this.foo = " + this.foo);   
            console.log("inner func:  self.foo = " + self.foo); 
        }());    
    }    
};    
myObject.func();

Output:

outer func:  this.foo = bar
outer func:  self.foo = bar
inner func:  this.foo = undefined
inner func:  self.foo = bar

Explaination:

The key here is this reference inside a function which is an object's property is that object itself. So first two logs print the expected result. Then you are using an IIFE and this reference inside IIFE is the global Object(Window object). Therefore this.foo means Window.foo there which is undefined. However self is accessable inside that function which has value equal to that object. Hence it prints the foo variable.

Answered By - Rohit Agrawal