use brackets in checkbox name when using php and javascript?

Question

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.

Answer 1

PHP has an unusual system for handling multiple form controls with the same name, it expects the names to include [] but it doesn't use them in the variable name.

JavaScript doesn't have that issue. The property will still have the brackets.

Of course, square brackets have special meaning in JS, so you can't use dot notation to access the property.

f['type[]'][i].checked

Answer 2

In javascript, you could use f['type[]'] instead of f.type. It's only php that changes [] to array.

Answer 3

Of course, you can also put a 'key' in between the square brackets, too (ie. give each field an actual unique name). Something like 'type[1]', 'type[2]' and 'type[3]'. PHP still throws it into an array (keyed by those numbers) and JS could access them, too.

Answer 4

You can always use document.getElementsByName() because it takes a string as argument.

Like this:

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