JAVASCRIPT

when i click on one checkbox check all checkboxes

function setAllCheckboxes(divId, sourceCheckbox) {
    divElement = document.getElementById(divId);
    inputElements = divElement.getElementsByTagName('input');
    for (i = 0; i < inputElements.length; i++) {
        if (inputElements[i].type != 'checkbox')
            continue;
        inputElements[i].checked = sourceCheckbox.checked;
    }
}

when i click on one checkbox check all checkboxes

<p><input onClick="setAllCheckboxes('actors', this);" type="checkbox" />All of them</p>
<div id="actors">
    <p><input type="checkbox" name="kevin" />Spacey, Kevin</p>
    <p><input type="checkbox" name="colin" />Firth, Colin</p>
    <p><input type="checkbox" name="scarlett" />Johansson, Scarlett</p>
</div>