Add Hours to a Date object in JavaScript

JavaScript itself has terrible Date/Time API's. Nonetheless, you can do this in pure JavaScript:

Date.prototype.addHours = function(h) {
  this.setTime(this.getTime() + (h*60*60*1000));
  return this;
}

Add Years to a Date in JavaScript

const date = new Date();

date.setFullYear(date.getFullYear() + 1);

console.log(date);