First the html. Don’t use divs for layout purposes.

<fieldset>
	// these will be affected by check all
<div>
<input id="checkall" type="checkbox" /> Check all</div>
<div>
<input type="checkbox" /> Checkbox</div>
<div>
<input type="checkbox" /> Checkbox</div>
<div>
<input type="checkbox" /> Checkbox</div>
</fieldset>
<fieldset>
	// these won't be affected by check all; different fieldset
<div>
<input type="checkbox" /> Checkbox</div>
<div>
<input type="checkbox" /> Checkbox</div>
<div>
<input type="checkbox" /> Checkbox</div>
</fieldset>

The original post divs are nonsense in terms of usability and semantics. Loose them as the original author just needed some BR tags.

<fieldset>
<input id="checkall" type="checkbox" /> Check all 
<input type="checkbox" /> Checkbox
<input type="checkbox" /> Checkbox
<input type="checkbox" /> Checkbox
</fieldset>
<fieldset>
	// these won't be affected by check all; different fieldset
<input type="checkbox" /> Checkbox
 
<input type="checkbox" /> Checkbox
 
<input type="checkbox" /> Checkbox
</fieldset>

This is the original javascript:

$(function () { // this line makes sure this code runs on page load
$('#checkall').click(function () {
$checkall = $(this); OK
$close = $checkall.parents('fieldset:eq(0)').find('input'); // this is called $close but it should be $elements or something
$checkall.attr('checked') !== true ? $close.removeAttr('checked') : $close.attr('checked', 'checked'); // see my version down
});
});

The javascript can be shortened and I preffer using native functions like is(), pseudoselectors like :checked, and boolean values when accepted instead of strings.


$('#checkall').click( function () {
var all= $(this).siblings();
$(this).is(':checked') ? all.attr('checked', true) : all.attr('checked', false);
});