Simple conditional

This conditional has a semicolon after the ( ) of the if statement. That is a null statement. so,

If the number is 9
    do nothing
do the alert()

Note that indentation does not tell JS what to do. It lets people read it easily. (Or not in this case.)

Enter a number, script checks for 9

  <script>
    function checkValue(){
      var val = document.getElementById("num").value;
      if (val == 9) ;
        alert("the number entered is 9");
    }
  </script>