text: export default function setDPR ($width = 750) {
      let d = document;
      const desWidth = $width;
      let _dpr = (1 / window.devicePixelRatio);
      const _MaxWidth = 414 * window.devicePixelRatio;
      const userAgent = navigator.userAgent;
      let widthStr = 'device-width';
      let isMobile = true;
      let iWidth = 0;
      let _html = d.getElementsByTagName('html')[0];
      if (userAgent.toLowerCase().indexOf('iphone') && userAgent.toLowerCase().indexOf('android')) {
          isMobile = false;//iWidth = _MaxWidth;
          widthStr = iWidth + 'px';
      }
      //todo:可能需要改成创建
      d.querySelector('[name="viewport"]').setAttribute('content',
          'width=' + widthStr + ' , initial-scale=' + _dpr + ', maximum-scale=' + _dpr + ', minimum-scale=' + _dpr + ', user-scalable=no');
      iWidth = Math.min(d.documentElement.clientWidth, window.innerWidth);
      if (!isMobile) iWidth = _MaxWidth;
      _html.style.fontSize = (((100 * iWidth) / desWidth)) + 'px';
      _html.dataset.dpr = window.devicePixelRatio;
      window.onresize = function () {
          setDPR();
      };
  }