howToClosure.js

function testClosure (){
  var x = 4;
  function closeX(){
    return x; // NB: x is not stored anywhere in the innermost function its a global variable
  }
  return closeX;
}

var checkLocalX = testClosure();

checkLocalX(); // this will return 4 even testClosure function has been closed because its local variable has now been bound within checkLocalX
              // because it has been bound as a closure within closeX