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) 
  }