JS: This vs No-this

no-this.js

 function foo() {
     var a = 2;
     function bar() {
         console.log(a);
     }

     bar();
 }
 foo()

this.js

 function foo() {
     var a = 2;
     function bar() {
         console.log(this.a);
     }

     this.bar();
 }
 foo()