js获取浏览器缩放比例

前几天在做项目的时候遇到浏览器缩放比例不为100%时，出来的页面不正常，于是找到了方法获取其比例来通知用户

function detectZoom (){
  var ratio = ,
    screen = window.screen,
    ua = navigator.userAgent.toLowerCase();

   if (window.devicePixelRatio !== undefined) {
      ratio = window.devicePixelRatio;
  }
  else if (~ua.indexOf('msie')) {
    if (screen.deviceXDPI && screen.logicalXDPI) {
      ratio = screen.deviceXDPI / screen.logicalXDPI;
    }
  }
  else if (window.outerWidth !== undefined && window.innerWidth !== undefined) {
    ratio = window.outerWidth / window.innerWidth;
  }

   if (ratio){
    ratio = Math.round(ratio * );
  }

   return ratio;
};

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