[Philip M]

There is quite a lot of code involved in this. Here is an outline to point you in the right direction. Essentially you need to convert your dates into Javascript Date Objects so that a comparison can be made.

But you must still ensure that the input is valid - only valid dates (not 31st February), in the right format dd/mm/yyyy, and that the end date is after the start date.
I leave that to you. I have invented data for the first three items.

This outline should move you forward:-

Event Title <input type = "text" id = "evtit">
Start Date dd/mm/yyyy <input type = "text" id = "stdate">
End Date dd/mm/yyyy <input type = "text" id = "endate">
<br><br>
<input type = "button" value = "Add Event" onclick = "add()">

<script type = "text/javascript">

var eventName = ["Event1", "Event2", "Event3"];
var startDate = ["05/01/2012", "12/02/2012", "08/03/2012"];
var endDate = ["12/01/2012", "20/02/2012", "19/03/2012"];

function add() {
var t = document.getElementById("evtit").value;
var sd = document.getElementById("stdate").value;
var ed = document.getElementById("endate").value;
// CHECK THE VALIDITY OF START AND END DATES
var ssplit = sd.split("/");
var esplit = ed.split("/");
var sobj = new Date(ssplit[2],ssplit[1]-1,ssplit[0]);  // months in Javascript are 0-11
var eobj = new Date(esplit[2],esplit[1]-1,esplit[0]);

for (var i =0; i<eventName.length; i++) {
var s = startDate[i].split("/");
var ss = new Date(s[2],s[1]-1,s[0]);  // months in Javascript are 0-11
var e = endDate[i].split("/");
var es = new Date(e[2],e[1]-1,e[0]);  // months in Javascript are 0-11
if ((eobj < ss) || (sobj > es)) {
alert ("OK - no overlap with Event " + i);
}
else {
var OK = false;
alert ("The event dates overlap with Event " + i");
return false;
}
}

// if the dates do not overlap add the details to the 3 arrays

}

</script>

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