JavaScript differences defining a function

Question

I just bought the newest version of "JavaScript: The Definitive Guide" and already have a question. :D

Are the following lines semantically the same:

var square = function(n){
 return n * n;
 };

and

function square(n){
 return n * n;
}

If yes, what are the advantages/disadvantages of using either of them?

Thanks for your help!

• Felix Kling: possible duplicate of What is the difference between a function expression vs declaration in Javascript?
• aydio: Thanks for pointing out, Felix. The differences between these two approaches are now clear.

Answer 1

Check this out:

a(); // prints 'A'
function a(){
 console.log('A');
};

and this:

b(); // throws error. b is not a function
var b = function() {
 console.log('B');
};

Did you notice the difference?

• aydio: Thanks for the simple explanation!

Answer 2

Yes, they do the exact same thing.

The main advantage of the first approach is that it gives you a reference to that function so that you could pass it to another function or attach it to an object if you need to.

• Aaron Digulla: I agree with the first sentence but if they both do the exact same thing, how can one be different from the other?
• Felix Kling: You can do the same with a function declaration (passing and assigning).

Answer 3

Difference is that in the first solution, you can do that :

var square = function(n){
 return n * n;
 };
// some code
square = function(n) { return n*n*n; }

you have reference to a function. On the other solution, the function is statically declared.

Disclaimer: need JS guru to tell me if I'm wrong =).

• aydio: Hi Clement, to be honest, I don't understand what the last line does. Could you kindly explain me the purpose of return nnn; when I want to calculate the square?
• Clement Herreman: Your example is a function that return the square value of a number, but that could be any other function, that does complicated, or really context-dependent work. Returning n*n*n for a square method is silly, but it is just for the example.