Global scoping of JavaScript variables

globalScope.js

<script type="text/javascript">

function fn(){ 
  //missing var declaration exposes 'x' to global scope
  x = "surprise!"

  //by using var 'y' remains private inside the instance of 'fn'
  var y = "really private!"    
} 

var inst = new fn()

console.log(x)

</script>