Enforce unique values based on multiple columns - sharepoint

Question

I'm trying to enforce unique values based on 3 columns. i'm trying for SharePoint online.
Lookup column
Choice
Calendar (only date)
I tried with below code, able to retrieve the existing values from the list but Calendar date selection is getting failed. not able to figure out what can be done. can anyone help on this,
<script type="text/javascript" src="/sites/Mysite/SiteAssets/jquery.min.js"></script><script type="text/javascript">
//variable to hold Ajax result
var dataResults;
var call = $.ajax({
url: _spPageContextInfo.webAbsoluteUrl + "/_api/Web/Lists/GetByTitle('Mylist')/Items?" + "$select=Title,Engagement,Period",
//Title is a lookup column
type: "GET",
dataType: "json",
async:false,
headers: {
Accept: "application/json;odata=verbose"
},
success: function(data) {
dataResults = data.d;
}
});
function PeriodValue(fullDate){
var orderDateString = "2016-10-19T22:00.00Z"; //UTC datetime value from REST response
var orderDate = new Date(orderDateString);
var value= TimeZoneUtilities.utcToLocalTime(_spPageContextInfo.webAbsoluteUrl,orderDate);
alert(value);
var dateValue=null,twoDigitDate=null,twoDigitMonth=null,twoDigitYear,currentDate=null;
dateValue = fullDate.split("T")[0];
twoDigitDate = dateValue.split("-")[2];
twoDigitMonth = dateValue.split("-")[1];
twoDigitYear = dateValue.split("-")[0];
currentDate = twoDigitDate + "/" + twoDigitMonth + "/" + twoDigitYear;
return currentDate;
}
//function to compare user input and existing data
function PreSaveAction(){
var ClientName = document.querySelector('[title="Client Name Required Field"]');
var engagement = document.querySelector('[title="Engagement Required Field"]');
var period = document.querySelector('[title="Period Required Field"]');
ClientName=ClientName.options[ClientName.selectedIndex].text;
engagement=engagement.options[engagement.selectedIndex].text;
period=period.value;
var c = null;
$.each(dataResults, function(i, item){
c = true;
$.each(item, function(i, dt){
console.log(dt.Engagement + ' ' + dt.Period + ' ' +dt.Title);
if (dt.Engagement == engagement && dt.Period == period && dt.Title==ClientName){
c = false;
alert("Already exist");
return c;
}
});
});
return c;
}
</script>​​