Question

In Pro JavaScript with Mootools book I have found the below line

The scoping rules for function expressions are a bit different from function 
declarations because they depend on variable scoping. Remember that in 
JavaScript, the var keyword defines a variable to be scoped locally, and 
omitting the keyword creates a global variable instead:    

As per my understanding I have written the below code and tried to check this

var a = function(){ 
   b = function(){ c = function(){ alert("b"); }; };
};
alert(typeof a); // Returned me 'function'
alert(typeof b); // Returned me 'undefined'
alert(typeof c); // Returned me 'undefined'

And I also tried below

var a = function(){ 
   var b = function(){ c = function(){ alert("b"); }; };
};
alert(typeof a); // Returned me 'function'
alert(typeof b); // Returned me 'undefined'
alert(typeof c); // Returned me 'undefined'​​

Could you please explain this to make me understand better. As per my understanding in first block of code b and c should be global variables.. But this is not happening in this case. Even I tried to invoke a() before alerts… Here is the fiddle. Please help me on this to understand scope better.

Answer 1

As per my understanding in first block of code b and c should be global variables

They are, but they won’t have values assigned to them until a is called (and until b is called in the case of c).

Here is the fiddle

That code is different. You have var b, which makes b a local variable and not a global.

---

var a = function(){ 
   b = function(){ c = function(){ alert("b"); }; };
};
a();
b();
alert(typeof a); 
alert(typeof b); 
alert(typeof c);