Select All checkboxes using jQuery

Question

I have the following html code:

Answer 1

 jQuery( function($){
    // add multiple select / deselect functionality
    $("#contact_select_all").click(function () {

        if($("#contact_select_all").is(":checked")){
            $('.noborder').prop('checked',true);
        }else
            $('.noborder').prop('checked',false);
    });

    // if all checkbox are selected, check the selectall checkbox
    $(".noborder").click(function(){

    if($(".noborder").length == $(".noborder:checked").length) {
        $("#contact_select_all").attr("checked", "checked");
    } else {
        $("#contact_select_all").removeAttr("checked");
    }

    });

});