Javascript] var vs no var

example global, local
<script>
var a=100, b=100;//global
(function(){var b=200;//local
 a=200;//global
 c=200;//new global
 (function(){
  b=300;//local
  c=300;//global
 }())
}())
alert(a+", "+b+", "+c);//200, 300, 300
</script>