closure function - returns global variable? - function

Question

i have the following question:
var a = 1;
function b(){
a = 10;
return;
function a(){}
}
// console.log("a equals to ",a); -> 1
b();
// console.log("now a equals to ", a) -> 1
so in this function i get 1 in both cases. Can somebody explain me why?
if i use const a = function() and of course put it before the return, the global variable will change to 10. Though now it does not.
My assumption is that this is not happening, because inside the function b, the variable a is a function. So the attempt a=10 will not work. But when i console.log(a) inside the b function the a is 10 and not a function.. Arghh!
Thanks in advance.
xx

Answer 1

so in this function i get 1 in both cases. Can somebody explain me why?
Variable a in the global scope and a inside b() belong to different scopes. Execution of b() happens in 2 phases:
Memory allocation: All variables declarations and functions in b() are first allocated memory. This is called hoisting.
This is how the global scope and local scope of b() would look like at this point: Local refers to the scope of b()
Local: {
a: function a()
}
Global: {
a: 1
}
Code execution: The line a = 10 will override and assign 10 to a inside b(). Right after this line the function returns. Note that b's execution does not modify a in the global scope. Thus, your code would log a as 1 even after b() finishes execution.
This is how the scopes would look like right before b() returns:
Local: {
a: 10
}
Global: {
a: 1
}
if i use const a = function() and of course put it before the return, the global variable will change to 10. Though now it does not.
To modify global variable a from b() you can remove function a, like this:
var a = 1;
function b() {
a = 10;
return;
}
console.log('a equals to ', a);
b();
console.log('now a equals to ', a);
Output:
a equals to 1
now a equals to 10
Why? Undeclared variables are always global in Javascript. This means that a declared in the global scope and a used inside b both reference the same variable. a=10 will therefore modify the a that was declared in the global scope.
This is how the scopes would look like:
Local: {
// no a
}
Global: {
a: 10
}