**Method a, **

 function CheckForm() {
             if(document.form1.trainingName.value==""){
                     alert(" Training course name cannot be empty! ");
                     document.form1.trainingName.focus();
                     return false;
             }
    }

**Method 2: jquery **

      function CheckForm() {
             var classLevel = $("#classLevel").val();
              var re = /^[1-9][0-9]*$/;
              if(!re.test(classLevel)&&classLevel.length>0){
              alert(" Please enter an integer greater than zero! ");
              $("#classLevel").focus();
              return false;
          }
    }