`document.form.button.click()` を使用せずに JavaScript でマウス クリック イベントをシミュレートするにはどうすればよいですか?

function simulate(element, eventName) {
  var options = extend(defaultOptions, arguments[2] || {});
  var oEvent, eventType = null;

  for (var name in eventMatchers) {
    if (eventMatchers[name].test(eventName)) { eventType = name; break; }
  }

  if (!eventType)
    throw new SyntaxError('Only HTMLEvents and MouseEvents interfaces are supported');

  if (document.createEvent) {
    oEvent = document.createEvent(eventType);
    if (eventType == 'HTMLEvents') {
      oEvent.initEvent(eventName, options.bubbles, options.cancelable);
    } else {
      oEvent.initMouseEvent(eventName, options.bubbles, options.cancelable, document.defaultView,
        options.button, options.pointerX, options.pointerY, options.pointerX, options.pointerY,
        options.ctrlKey, options.altKey, options.shiftKey, options.metaKey, options.button, element);
    }
    element.dispatchEvent(oEvent);
  } else {
    options.clientX = options.pointerX;
    options.clientY = options.pointerY;
    var evt = document.createEventObject();
    oEvent = extend(evt, options);
    element.fireEvent('on' + eventName, oEvent);
  }
  return element;
}

simulate(document.getElementById("btn"), "click");

simulate(document.getElementById("btn"), "click", { pointerX: 123, pointerY: 321 });