warn user if all checkboxes are unchecked

Question

I have a form with a series of checkboxes. I want to warn the user, after they hit submit, if ALL of the checkboxes are unchecked. I'm using the following code to report all of the values of the checkboxes:

$('[id^=leg_rider]').filter(':checked');

This seems to work. However, when I try to check to see if the returned object is empty, it doesn't seem to work. This is what I'm trying:

        $("#set_pref_submit").click(function() {
        var legchecked = $('[id^=leg_rider]').filter(':checked');
        if (!legchecked){ alert("no riders")};
    });

Any suggestions are appreciated. Thanks!

Answer 1

You can use jQuery object's length property:

$("#set_pref_submit").click(function() {
    var legchecked = $('input[id^=leg_rider]:checked').length;
    if (legchecked){ alert("no riders")};
});

Answer 2

Working Demo : http://jsfiddle.net/MrkfW/

Try this: using .change api as well so it keep the track :)

API: http://api.jquery.com/change/

$("input[type='checkbox'][id^=leg_rider]").change(function(){
    var a = $("input[type='checkbox'][id^=leg_rider]");
    if(a.length == a.filter(":checked").length){
        alert('all checked');
    } else {
        alert('not all checked');
    }
});