สอบถามเรื่อง Javascript ครับ สวัสดีครับพี่ๆ ผมขอถามเกี่ยวกับ JavaScript หน่อยครับ

  <?php
		
		  $query3="SELECT students.stdid,students.stdnamelao,students.stdsurnamelao,students.gender FROM students INNER JOIN tbclass ON students.classid=tbclass.classid INNER JOIN departments on students.deptid=departments.deptid INNER JOIN majors ON students.majorid=majors.majorid INNER JOIN taughtby on tbclass.classid=taughtby.classid WHERE tbclass.classid='$vl5' AND students.yearid='$vl4' and majors.majorid='$vl3' AND taughtby.tid='$session_id' AND taughtby.subid='$vl1' ";
				$result3=mysql_query($query3)or die(mysql_error());
				 $c=0;
				while ($rows3=mysql_fetch_array($result3)) {
					$Stid= $rows3['stdid'];
					$Stnamelao= $rows3['stdnamelao'];
					$Stsurlao= $rows3['stdsurnamelao'];
					$Gd= $rows3['gender'];
					
					?>
                  <tr class="odd gradeX">
                    <td><?php echo $Stid ;?></td>
                    <input type="hidden" name="tid[]" value="<?php echo $Stid ;?>"/>
                    <td><?php echo $Stnamelao; ?></td>
                    <input type="hidden" name="stnlao[]" value="<?php echo $Stnamelao ;?>"/>
                    <td><?php echo $Stsurlao; ?></td>
                    <input type="hidden" name="stslao[]" value="<?php echo $Stsurlao ;?>"/>
                    <td ><?php echo $Gd; ?></td>
                    <input type="hidden" name="Gd[]" value="<?php echo $Gd ;?>"/>
                    <td><input  type="text" name="score" size="3"  id="score_" onKeyUp="calculate()"  onKeyPress="CheckNum()" maxlength="3" ></td>
                    <td><input type="text"  name="score2" size="3" id="score2_"onKeyUp="calculate()"  onKeyPress="CheckNum()"maxlength="3"  class="form-control " ></td>
                    <td><input type="text" name="score3" size="3" id="score3_" onKeyUp="calculate()"  onKeyPress="CheckNum()"maxlength="3"  class="form-control "></td>
                    <td><input type="text" name="scorefull" id="scorefull" maxlength="3"  size="3" class="form-control "readonly /></td>
                    <input name="scoure%" type="hidden" id="scoure4" readonly maxlength="3"  class="form-control " />
                    <td><input class="form-control "readonly id="scoregrad" maxlength="3" type="text" name="scoregrad"  size="3" disabled   ></td>
                    <script type='text/javascript'>
function  checkNumber(elm){
 if(elm.value>50){
alert('can not input over 50');
elm.value='';
}
}
</script> 
                    <script language="javascript">
function CheckNum(){
    if (event.keyCode < 48 || event.keyCode > 57){
          event.returnValue = false;
        }
  }
</script> 
                    <script language="javascript">
 function calculate()
  {
    var scorefull_ = 0;
    var scoregrad = "-";
    var scoure4_ = "-";

	
	 var score  = parseInt(document.getElementById('score_').value);
    var score2 = parseInt(document.getElementById('score2_' ).value);
    var score3 = parseInt(document.getElementById('score3_').value);
	var table = document.getElementById('example');    
var rowCount = table.rows.length;    


    if ( isNaN(score) )
    {
      score = 0;
    }
    if ( isNaN(score2) )
    {
      score2 = 0;
    }
    if ( isNaN(score3) )
    {
      score3 = 0;
    }
   
    
    scorefull_=score+score2+score3;

    if (scorefull_) {
    scoure4_ = (scorefull_ /100)*80;
  document.getElementById('scoure4').value = scoure4_;

    }

        if (scorefull_>=80) {

     document.getElementById('scoregrad').value = "A";
  } 
  else 
   if (scorefull_>=75) {

     document.getElementById('scoregrad').value = "B+";
  } else 
   if (scorefull_>=70) {

     document.getElementById('scoregrad').value = "B";
  } else 
   if (scorefull_>=65) {

     document.getElementById('scoregrad').value = "C+";
  }
  else 
   if (scorefull_>=60) {

     document.getElementById('scoregrad').value = "C";
  }
  else 
   if (scorefull_>=55) {

     document.getElementById('scoregrad').value = "D+";
	 
  }else 
   if (scorefull_>=50) {

     document.getElementById('scoregrad').value = "D";
  }
    document.getElementById('scorefull').value = scorefull_;

  if(scorefull_>100) {
        alert('can not input over 100');
        if (score > 0 ) {
          score5 = scorefull_ - 100;
          score6 = score- score5; 
           document.getElementById('score_').value =score6;
        }

         else if ( score2 > 0) {
          score5 = scorefull_ - 100;
          score7 = score2- score5; 
    document.getElementById('score2_').value =score7; 
  }
         else if ( score3 > 0) {
          score5 = scorefull_ - 100;
          score8 = score3- score5; 
        document.getElementById('score3_').value =score8;
      }
    document.getElementById('scorefull').value =100; 

                }
  }
                
           </script>