en.javascript.info/1-js/9-object-inheritance/15-class-inheritance/4-clock-class-extended/extended-clock.js

function ExtendedClock(options) {
  Clock.apply(this, arguments);
  this._precision = +options.precision || 1000;
}

ExtendedClock.prototype = Object.create(Clock.prototype);

ExtendedClock.prototype.start = function() {
  this._render();
  var self = this;
  this._timer = setInterval(function() {
    self._render();
  }, this._precision);
};