MouseEvent(String type, {Window view, int detail: 0, int screenX: 0, int screenY: 0, int clientX: 0, int clientY: 0, int button: 0, bool canBubble: true, bool cancelable: true, bool ctrlKey: false, bool altKey: false, bool shiftKey: false, bool metaKey: false, EventTarget relatedTarget})

Source

factory MouseEvent(String type,
    {Window view, int detail: 0, int screenX: 0, int screenY: 0,
    int clientX: 0, int clientY: 0, int button: 0, bool canBubble: true,
    bool cancelable: true, bool ctrlKey: false, bool altKey: false,
    bool shiftKey: false, bool metaKey: false, EventTarget relatedTarget}) {

  if (view == null) {
    view = window;
  }
  var event = document._createEvent('MouseEvent');
  event._initMouseEvent(type, canBubble, cancelable, view, detail,
      screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey, metaKey,
      button, relatedTarget);
  return event;
}