gistfile1.js

function makeObservable(object) {
  var _listeners = {},
      _slice = [].slice;
  
  function addEventListener(eventName, handler) {
    var handlers = _listeners[eventName];
    if (!handlers) {
      handlers = _listeners[eventName] = [];
    }
    handlers.push(handler);
    return object;
  }
  
  function fireEvent(eventName) {
    var handlers = _listeners[eventName],
        args;
    if (handlers) {
      args = _slice.call(arguments, 1);
      for (var i = 0, h; h = handlers[i]; i++) {
        h.apply(object, args);
      }
    }
    return object;
  }
  
  object.addEventListener = addEventListener;
  object.fireEvent = fireEvent;
}