TabChoices

gistfile1.html

<script type="text/javascript">
function checkboxlimit(checkgroup, limit){
    var checkgroup=checkgroup
    var limit=limit
    for (var i=0; i<checkgroup.length; i++){
        checkgroup[i].onclick=function(){
        var checkedcount=0
        for (var i=0; i<checkgroup.length; i++)
            checkedcount+=(checkgroup[i].checked)? 1 : 0
        if (checkedcount>limit){
            alert("You can only select a maximum of "+limit+" checkboxes")
            this.checked=false
            }
        }
    }
}
</script>

<form method="post" id="thanks" name="thanks">

<!--If I change "tabChoices[]" to "tabChoices" (without the array) it works fine -->
<input type="checkbox" name="tabChoices[]" value="EXAMPLE 1" id="tabChoices_1"/>
<input type="checkbox" name="tabChoices[]" value="EXAMPLE 2" id="tabChoices_2"/>
<input type="checkbox" name="tabChoices[]" value="EXAMPLE 3" id="tabChoices_3"/>
</form>

<!--
  // document.forms.thanks.tabChoices doesn't work (will be undefined) as the checkboxes are called "tabChoices[]"
  // javascript objects can be accessed using dot notation or like so:
-->
<script type="text/javascript">checkboxlimit(document.forms.thanks["tabChoices[]"], 2)</script>

<!-- 
  // Still, the best thing would be to rename the collection.  [] denotes an array in jaavscript and looks confusing as a property/object name
-->