Update the configuration (2)

var conf = {
  dateRange: [
    new Date('2017-01-01'),
    new Date('2018-01-01'),
  ],
  data: [
    // ...
  ]
};

var t = new Zeitline.Timeline(conf);
t.render();

buttonNext.addEventListener('click', (e) => {
  var diff = conf.dateRange[1] - conf.dateRange[0];
  conf.dateRange[0] -= -diff;
  conf.dateRange[1] -= -diff;
  t.update(conf);
}, false);

buttonPrev.addEventListener('click', (e) => {
  var diff = conf.dateRange[1] - conf.dateRange[0];
  conf.dateRange[0] -= diff;
  conf.dateRange[1] -= diff;
  t.update(conf);
}, false);