If you would like to implement Select All/UnSelect check-boxes with jquery please follow the below code::

<table class="demo-table">
<tr><td><input type="checkbox" name="selectall" id="selectall">Select All</td></tr>
<tr><td><input type="checkbox" name="select[]" class="ab" value="1"></td></tr>
<tr><td><input type="checkbox" name="select[]" class="ab" value="2"></td></tr>
<tr><td><input type="checkbox" name="select[]" class="ab" value="3"></td></tr>
</table>
<script>
$(document).ready(function () {
        $("#selectall").change(function () {            
           if(this.checked){
                $('.ab').each(function(){
                    this.checked = true;
                })
            }else{
                $('.ab').each(function(){
                    this.checked = false;
                })
            }
        });

    });
</script>