Question

I have this HTML code

<input type="checkbox" name="city_pref[]" id="city_all" value="0" checked /><label for="city_all">All</label>
<input type="checkbox" name="city_pref[]" id="city_pref_1" value="Chicago" /><label for="city_pref_1">Chicago</label>
<input type="checkbox" name="city_pref[]" id="city_pref_2" value="Texas" /><label for="city_pref_2">Texas</label>

And, I have placed my code in a fiddle, which is working correctly. What I really want to do is, when none of the checkboxes are selected, then I want the all checkbox to get selected automatically.

Answer 1

try the following:

$('input[type=checkbox]').change(function(){
    if ($('input[type=checkbox]:checked').length == 0) {
       $('#city_all').prop('checked', true)
    }   
})

DEMO