Because although 0 is a typeof integer but when you return 0 . It will not been include in the array as it is a false value in javascript.
Basically javascript considered 0 as false.
But in the same code if you write this

if(typeof(a)=='number'){
return true;
}

It will include 0 too.

In the case of typeof a == "number" ,it statisfy the condition as it is a interger.

Hope it would be helpful to you.

how do this code deal with the puncuations?

can someone please explain this to me

can someone please explain this to me

can someone please explain this to me

can someone please explain this to me

When i use return statment directly like this:
return typeof a == "number";(this works fine)
But when I put it inside if statment like this:
if(typeof(a)=='number'){
return a;
}
it does not return 0 .. please explain this