Working with dates and time in WIX Code?

Hi Andreas,
Would you please explain what you are doing.
I get red dots errors saying “tt is undefined”.
Here is my code
The field I need to add to = quoteDate

var quoteDate = new Date(tt); 
var newdate = new Date(quoteDate); 

newdate.setDate(newdate.getDate() + 3); // Adding three days 

var dd = newdate.getDate(); 
var mm = newdate.getMonth() + 1; 
var y = newdate.getFullYear(); 
var someFormattedDate = dd + '/' + mm + '/' + y;