Check all other checkboxes when one is checked

Question

I have a form and group of checkboxes in it. (These checkboxes are dynamically created but I dont think it is important for this question). The code that generates them look

Answer 1

Thanks to @Ashish, I have expanded it slightly to allow the "master" checkbox to be automatically checked or unchecked, if you manually tick all the sub checkboxes.

FIDDLE

HTML

Select all


    checkbox1

    checkbox2

    checkbox3

    checkbox4

SCRIPT

$('.selectall').click(function() {
    if ($(this).is(':checked')) {
        $('input:checkbox').prop('checked', true);
    } else {
        $('input:checkbox').prop('checked', false);
    }
});

And now add this to manage the master checkbox as well...

$("input[type='checkbox'].justone").change(function(){
    var a = $("input[type='checkbox'].justone");
    if(a.length == a.filter(":checked").length){
        $('.selectall').prop('checked', true);
    }
    else {
        $('.selectall').prop('checked', false);
    }
});