Tracker Object to track time - including pause and resume functionality

tracker.js

/* 
   LICENSE: MIT
   Created by: Anders Holm-Jensen
   Website: allora.dk 
   Date: 25-oct-2017
   */
const timestamp = () => ( Math.round( new Date() * 1 / 1000) );

let tracker = {
  data: {
    state: 0, // 0 = stopped, 1 = active, 2 = paused
    duration: 0,
    pausedbuffer: 0,
    started: 0,
    ended: 0,
    timer: null
  },

  begin: function() {
    if(this.data.state !== 0) return false;
    this.data.state = 1;
    this.data.duration = 0;
    this.data.pausedbuffer = 0;
    this.data.ended = 0;
    this.data.started = timestamp();
    this.data.timer = setInterval(function() {
      if(tracker.data.state === 1) {
        console.log(Math.round(new Date() * 1 / 1000), 'tracking');
      }
    }, 1000);
  },

  stop: function() {
    if(this.data.state === 0) return false;
    this.data.state = 0;
    this.data.ended = timestamp();
    this.data.timer = clearInterval(this.data.timer);
    this.show();
  },

  pause: function() {
    if(this.data.state !== 1) return false;
    this.data.state = 2;
    this.data.ended = timestamp(); // use ended as placeholder for paused time
  },

  resume: function() {
    if(this.data.state !== 2) return false;
    this.data.state = 1;
    this.data.pausedbuffer = this.data.pausedbuffer + (timestamp() - this.data.ended);
    this.data.ended = 0; // clear paused time placeholder
  },

  // helper functions
  show: function() {
    let duration = this.data.ended - this.data.started - this.data.pausedbuffer;
    this.data.duration = (duration > 0) ? duration : 0;
    console.table(this.data);
    return this.data;
  },

  toggle: function() {
    if(this.data.state === 0) return this.begin();
    if(this.data.state === 1) return this.pause();
    if(this.data.state === 2) return this.resume();
  },

  isactive: function() {
    return this.data.active;
  }
}

/*
Start it by calling tracker.toggle()
Toggle between tracking/pause using tracker.toggle()
End trcaking by calling tracker.stop()

See tracking result by calling tracker.show()
*/