If you have a list of checkboxes or radio buttons and want to see if any of them were selected, JQuery makes it simple:

if (!(jQuery("input[@name=<input_name>]:checked").length)) {
    alert('Please select something!');
    return false;
}

return true;

Simply replace <input_name> with the name of your checkboxes/radio buttons. Calling code example:

<form action="someFile.php" method="post" onSubmit="return validateCheckboxes();">

    <input type="checkbox" id="checkbox_id_1" name="checkboxIds[]" value="1"/>
    <input type="checkbox" id="checkbox_id_2" name="checkboxIds[]" value="2"/>
    <input type="checkbox" id="checkbox_id_3" name="checkboxIds[]" value="3"/>
    

So the final javascript would like like:

function validateCheckboxes()
{
    if (!(jQuery("input[@name=checkboxIds]:checked").length)) {
        alert('Please select something!');
        return false;
    }
}
return true;

You can also use specific dom ids, but if you are iterating over a list and echoing out checkboxes/radio buttons I wouldn’t recommend it, as demonstrated above you can hook into multiple inputs by using name.