[]touches一直为undefined

Laya.stage.on(Laya.Event.MOUSE_DOWN, this, onCtrlMoveRockerTouchDown);

......
 

function onCtrlMoveRockerTouchDown(e) {
    console.log("onCtrlMoveRockerTouchDown()");

    var touches = e.touches;

    if(touches) {
    ...取出前两个touch进行计算
    }
}
 
请问为什么我的touches一直都是undefined