Validate 2 list boxes, one is multiselect, one is singleselect

<head>
      <script language="javascript">

            function validateListBox(){
                var lb = document.getElementById('mySelect');
                var count1 = 0;
                arrTexts = new Array();

                for(var i=0; i<lb.length; i++)  {
                    if(lb[i] != 0){
                      count1++;
                    }

                }

                if(count1 != 0){
                    alert('empty');
                    return true;
                }

                return false;        
            }

          </script>
          <noscript>Your browser does not support JavaScript!</noscript>
     </head>

One list box contains "student" IDs, and the other one contains "courses" IDs. I want the user to assign students to courses by selecting the corresponding IDs and I will enter the user's input into a bridge table. This bridge table links between "students"-"courses".

I want to restrict the user to choose 1 student-> to 1/more courses per form entry. NOT many students-> 1/many courses.

I've seen on Google that function must be call with onClick, other said with onSubmit. And many examples but none worked for me.

In the form I call it as so:

<form action = "AssignmentsList.jsp" method="post" name="entry">

.................

<input type="button" value = "Link" onClick = "validateListBox()"/>

.................

View Answers

July 22, 2012 at 11:19 PM

I finally find out to be:

<script language="javascript">

            function validate(){
                var k=0;
                if (entry.elements["sid"].selectedIndex == -1) {
                      k++;
                      alert('You cannot select one side only');
                      return false;
                }

                if (entry.elements["cid"].selectedIndex == -1) {
                      k++;
                      alert('You cannot select one side only');
                      return false;
                }

                if(k == 0){
                  return true;
                }

                return false;
            }

          </script>

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