A simple Time object that allows you to add, subtract and print times.

Time.jsx

export function Time(hours, minutes) {
  this.h = hours;
  this.m = minutes;

  this.add = (h, m) => {
    this.h = (this.h + h) % 24;
    this.h = this.h + Math.floor((this.m + m) / 60);
    this.m = (this.m + m) % 60;
    return this; // for method chaining
  };
  this.subtract = (h, m) => {
    this.h = (24 + (this.h - h)) % 24;
    this.h = this.h - Math.floor((59 + (m - this.m)) / 60);
    this.m = (60 + (this.m - m)) % 60;
    return this;
  };
  this.toString = () => `0${(this.h)}`.slice(-2).concat(':').concat(`0${(this.m)}`.slice(-2));
}