1 var foo = 0;
 2 (function fn1(){
 3     foo = 1;
 4     console.log(foo);//1
 5     (function fn2(){
 6         var foo = 2;
 7         console.log(foo);//2
 8         (function fn3(){
 9             foo = 3;
10             console.log(foo);//3
11         }());
12     }());
13 }());
14 console.log(foo);//1

1 (function fn1(){
2     (function fn2(){
3         (function fn3(){
4             foo = 3;
5         }());
6     }());
7 }());
8 console.log(foo);//3

1 (function fn1(){
2     (function fn2(){
3         var foo;
4         (function fn3(){
5             foo = 3;
6         }());
7     }());
8 }());
9 console.log(foo);//Uncaught ReferenceError: foo is not defined