How to find control in javascript client custom validator

Posted on 2008-10-14
Last Modified: 2012-06-27
Goal is to validate on the client side (javascript) that a listbox has either no selections or at least a minimum number of rows selected.
I can sneak in the minimum number of rows, but need assistance finding the listbox, given the source or args parameters.

<script type="text/javascript" >

  function cvAnswer_7_2_4MinLengthListBox_ClientValidate(source, args) {





    var regex = /^\D*\d+_(\d+)_/;

    var result =;

    var minLength = parseInt(result[1], 10);

    var lbx = document.getElementById(;




    var selectedCount = 0;


    var i;


    for (i = 0; i < lbx.options.length; i++) {

      if (lbx.options[i].selected) {





    args.IsValid = (selectedCount >= minLength);





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Question by:brotherbill999
1 Comment

Accepted Solution

brotherbill999 earned 0 total points
Comment Utility
To find listBox, use: source.controltovalidate
Note that on Server side, it is ControlToValidate, but on javascript side it is all lowercase.

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