IOS 禁止缩放页面的实现方法

<meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0;" name="viewport" /> 

window.onload=function () {     document.addEventListener('touchstart',function (event) {       if(event.touches.length>1){         event.preventDefault();       }     })     var lastTouchEnd=0;     document.addEventListener('touchend',function (event) {       var now=(new Date()).getTime();       if(now-lastTouchEnd<=300){         event.preventDefault();       }       lastTouchEnd=now;     },false)   }