Remove last selected element from the multiple select if user select more than 3 option using jquery

Question

I need to select only 3 options from the multiple select. If user selects more than 3 options than the last selected element should be replaced by the new one clicked.

I have a example as follows:

<select multiple id='testbox'>
      <option value='1'>First Option</option>
      <option value='2'>Second Option</option>
      <option value='3'>Third Option</option>
      <option value='4'>Fourth Option</option>
      <option value='5'>Fifth Option</option>
      <option value='6'>Sixth Option</option>
      <option value='7'>Seventh Option</option>
      <option value='8'>Eighth Option</option>
      <option value='9'>Ninth Option</option>
      <option value='10'>Tenth Option</option>
    </select>

When user selects

First option
Second option
Third option

Now he reaches max selection limit 3 .If he click on the another option like Tenth Option I need to remove Third option and get selected Tenth option

For that i tried this but no idea how I can achieve my goal

<script type="text/javascript">
    google.load("jquery", "1");

    $(document).ready(function() {
        //alert("1111");
      var last_valid_selection = null;

      $('#testbox').change(function(event) {
        if ($(this).val().length > 2) {
          alert('You can only choose 2!');
          $(this).val(last_valid_selection);
        } else {
          last_valid_selection = $(this).val();
          latest_value = $("option:selected:last",this).val()
          alert(latest_value);
        }
      });

    });
    </script>

Please suggest some idea or solution.

Answer 1

This works quite nicely:

var lastSelected;

$("#testbox").change(function() {
    var countSelected = $(this).find("option:selected").length;

    if (countSelected > 3) {
        $(this).find("option[value='" + lastSelected + "']").removeAttr("selected");
    }
});

$("#testbox option").click(function() {
    lastSelected = this.value;
});

I had to set a global variable lastSelected as well as an options click event to capture the actual last option clicked ( this.value in the change event was giving me the top selected option, not the actual last option).

Demo: http://jsfiddle.net/JAysB/1/

Answer 2

Well, I don't like jQuery, so I've developed the same ( fiddle ), but in pure, vanilla, easy-to-read JavaScript:

document.getElementById('testbox').selopt=new Array();
document.getElementById('testbox').onchange=function(){
    for(i=0; i<this.childNodes.length; i++)
        if(this.childNodes[i].tagName!='OPTION')
            continue;
        else{
            if(this.childNodes[i].selected &&
               this.selopt.indexOf(this.childNodes[i])<0)
                this.selopt.push(this.childNodes[i]);
        }
    if(this.selopt.length==4)
        this.selopt.splice(2,1)[0].selected=false;
}

PS No global variables! :P

Answer 3

var lastOpt;
$('#testbox option').click(function () {
    lastOpt = $(this).index();
});
$('#testbox').change(function () {
    if ($('option:selected', this).length > 3) {
        $(' option:eq(' + lastOpt + ')', this).removeAttr('selected');
    }
});

JSFIDDLE