how do I make an option to select all and it automatically ticks all the boxes

[cretam]

Hi,
I have a form where the user picks a category which then displays a second level of tickboxes. How do I add an extra tick box that says 'Select all' and when it is chosen all the boxes are ticked.
Thank you in advance.

[dagon]

javascript, not php

[JPnyc]

it will be something like:

function checkAll() {
var boxes = document.forms[0].elements;
for(var i = 1; i < boxes.length; i++) {
if(boxes[0].checked) {
boxes.checked= true;
}
else {
boxes.checked= false;
}
}
}


then call the function onclick of the very first checkbox.