手机端（H5）图片下载

在 h5 端转 base64 下载图片，在红米手机浏览器中下载，但是没有资源输出，所以增加了安卓判断，把 base64 转了 blob 进行下载

base64ToBlob(code) {
        let parts = code.split(';base64,');
        let contentType = parts[0].split(':')[1];
        let raw = window.atob(parts[1]);
        let rawLength = raw.length;
        let uInt8Array = new Uint8Array(rawLength);
        for (let i = 0; i < rawLength; ++i) {
          uInt8Array[i] = raw.charCodeAt(i);
        }
        return new Blob([uInt8Array], {
          type: contentType
        });
      },
      // 下载图片
      loadCode(imgsrc, name) {
        let image = new Image();
        // 解决跨域 Canvas 污染问题
        image.setAttribute('crossOrigin', 'anonymous');
        // console.log('imgsrc--', image);
        image.src = imgsrc;
        const that = this;
        image.onload = function () {
          let canvas = document.createElement('canvas');
          canvas.width = image.width;
          canvas.height = image.height;
          let context = canvas.getContext('2d');
          context.drawImage(image, 0, 0, image.width, image.height);
          let url = canvas.toDataURL('image/png'); // 得到图片的base64编码数据
          let a = document.createElement('a');
          let event = new MouseEvent('click');
          a.download = name || 'image-' + new Date().getTime();
          // 区别 iso 和 android 下载方式
          if (that.curSystem === 'android') {
            let blob = that.base64ToBlob(url);
            a.href = URL.createObjectURL(blob);
          } else {
            a.href = url;
          }
          a.dispatchEvent(event); // 触发a的单击事件
        };
      },