SharePoint Form field date validation using javascript

<script language=”javascript” type=”text/javascript”>
function PreSaveAction()
{
var date1 = getTagFromIdentifierAndTitle(“INPUT”,”DateTimeFieldDate”,”Start Date”);
var date2 = getTagFromIdentifierAndTitle(“INPUT”,”DateTimeFieldDate”,”End Date”);
var arrDate1 = date1.value.split(“/”);
var useDate1 = new Date(arrDate1[2], arrDate1[1]-1, arrDate1[0]);
var arrDate2 = date2.value.split(“/”);
var useDate2 = new Date(arrDate2[2], arrDate2[1]-1, arrDate2[0]);
if(useDate1 > useDate2)
{
alert(“The End Date cannot happen earlier than the Start Date”);
return false; // Cancel the item save process
}
return true; // OK to proceed with the save item
}
function getTagFromIdentifierAndTitle(tagName, identifier, title) {
var len = identifier.length;
var tags = document.getElementsByTagName(tagName);
for (var i=0; i < tags.length; i++) {
var tempString = tags[i].id;
if (tags[i].title == title && (identifier == "" || tempString.indexOf(identifier) == tempString.length – len)) {
return tags[i];
}
}
return null;
}
</script>