移动端，JS判断滑到页面顶部下滑进行操作

和底部上滑操作，这个比较简单，原生无特效

topPullDownDo:function(){var sY,eY,_h,slideNum,UA =navigator.userAgent,isUC=UA.indexOf("UCBrowser")!=-1||UA.indexOf("Baidu")!=-1||UA.indexOf("MQQBrowser")!=-1;slideNum=isUC?6:60;doc.addEventListener("touchstart",function(evt){sY=evt.touches[0].pageY;},false);isUC&&doc.addEventListener("touchmove",function(evt){_h&&clearTimeout(_h);_h=setTimeout(function(){touchEndHandle(evt);},1);},false);doc.addEventListener("touchend",touchEndHandle,false);function touchEndHandle(evt){eY=evt.changedTouches[0].pageY;if(eY-sY>slideNum&&win.pageYOffset<=0){callback();}}
}