Square bracket in checkbox name

i have a form with checkboxes like this:

    <input type=\"checkbox\" name=\"type[]\" value=\"1\" />Fast Food<br>
    <input type=\"checkbox\" name=\"type[]\" value=\"2\" />Table Service<br>
    <input type=\"checkbox\" name=\"type[]\" value=\"3\" />Cafeteria<br>

when i use the brackets in the name (type[]), my php works:

    $type=$_POST[\'type\'];

    echo \"types are:\";
for ( $counter = 0; $counter < sizeof($type); $counter += 1) {
    echo \"<br>\".$type[$counter];
}

but my javascript doesn\'t work:

    var f = document.addform;
    for (var i=0;i<f.type.length;i++){
        if(f.type[i].checked==true){
            break;
        }
        if(i==(f.type.length-1)){
            alert(\"No categories entered!\");
            valid=false;
        }
    }

however, if i take away the brackets:

<input type=\"checkbox\" name=\"type\" value=\"1\" />Fast Food<br>

then the PHP doesn\'t work but the javascript does.

what\'s going on here? what should i use?

thanks.