doesn't deslect checkbox

while calling this script in code behind when click caccel button . It doesn't deselect check box. It shows alert message

function Confirm(chkAction) {
// var OBJID = document.getElementById(chkAction);
var checkUpdate = confirm("test");
if (checkUpdate) {
document.getElementById(chkAction).checked = true;
}
else {
document.getElementById(chkAction).checked = false;

}
}

Raghu.M.V.
Software Engineer.