javascript error because of global scope variables

Question

var x = 3;
(function (){
  console.log('before', x);
  var x = 7;
  console.log('after', x);
  return ;
})();

In the above code var X is initialized globally. So inside the function the first console.log should print "before 3" but i don't get it. The reason is that i am trying to re-declare the global variable.

Can somebody explain why this is happening?

Answer 1

In the above code var X is initialized globally. so inside the function the first console.log should print "before 3".

No, it should print before undefined, because var takes effect from the beginning of the function regardless of where you write it.

Your code is exactly the same as this:

var x = 3;
(function (){
 var x;

 console.log('before', x);
 x = 7;
 console.log('after', x);
 return ;
})();

And of course, variables start with the value undefined.

Details: Poor misunderstood var