JSFiddle - React, Tailwind, and code Playground

JavaScript

var getDays = function(startDate, endDate){
   var ONE_DAY = 1000 * 60 * 60 * 24;
   var difference = endDate.getTime() - startDate.getTime();
   return Math.round(difference / ONE_DAY);
}

alert(getDays(new Date('2011/10/17 00:00:00 UTC'), new Date()) + " days since launch");