JavaScript hoisting explanation

Question

What is the difference between below snippets?

var a = 0;
function b(){
    a = 10;
    return function a(){};
}
b();
console.log(a);  // => 10
         


        

Answer 1

return
function a() {}

is same as

return;
function a() {}

after automatic semicolon insertion. In second case, function a is moved to the top of its scope. The code is same as

var a = 0;

function b() {
  function a() {};
  a = 10;
  return;
}
b();
console.log(a);

As a inside b() is inner function and then overriden, it is not accessible from outside of b().

Here is the demo to understand how the hoisting works.

var a = 0;

function b() {
  console.log(a); // function
  a = 10;
  console.log(a); // 10
  return

  function a() {};
}
console.log(b()); // undefined
console.log(a);