Adding and Subtracting Dates with JavaScript

JavaScript

var processedAtDateTime = new Date("2017-11-29T19:46:13Z");
var nowDateTime = new Date();

var differenceDateTime = (nowDateTime-processedAtDateTime)/1000/60/60/24;
console.log(differenceDateTime);

if (differenceDateTime * 24 < 1) {
  differenceDateTime /= (24*60);
  console.log("Difference less than 1 hour. Convert minutes.");
  console.log(differenceDateTime);
} else if (differenceDateTime < 1) {
  differenceDateTime /= 24;
  console.log("Difference less than 1 day. Convert hours.");
  console.log(differenceDateTime);
} else {
  console.log("Difference greater than 1 day. Keep days.");
  console.log(differenceDateTime);
}
differenceDateTime = Math.floor(differenceDateTime);
console.log(differenceDateTime);