<script type="text/javascript">

     var num = 1

     if( num == 3 ){

         alert("1");

     }

     else if( num == 2 )

    {

         alert("2");

     }

     else if( num == 1 )

    {

         alert("1");

     }

     else

    {

         alert("0");

     }

</script>

<script type="text/javascript">

     var num = 1

     switch(num){

      case 1:

              alert('1');

              break;

     case 2:

              alert('2');

              break;

     case 3:

              alert('3');

              break;

    default:

             alert('0');

    }

</script>