[Richard M]

Thanks guys.

So basically I should do this?

function execute(id) {
var taskitem = document.getElementById("taskitem_section" + id);
var msg_done = document.getElementById("msg_done" + id);
var title = document.getElementById("title" + id);
var check = document.getElementById("check" + id);
if (msg_done.style.display="none") {
	taskitem.style.opacity="0.3";
	title.style.textDecoration="line-through";
	msg_done.style.display="inline";
}
else {
	taskitem.style.opacity="1";
	title.style.textDecoration="none";
	msg_done.style.display="none";
}