base64 文件转换

1、将base64转换为 file 对象

function () {
    var arr = image.split(','), mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
    while(n--){
      u8arr[n] = bstr.charCodeAt(n);
    }
    let file = new File([u8arr], i, {type:mime});
}

2、将 file 对象转换为 base64 图片

putImgData(file) {
  let Orientation = null;
  let self = this;
  if (file) {
    //获取照片方向角属性
    Exif.getData(file, function () {
      Exif.getAllTags(this);
      Orientation = Exif.getTag(this, 'Orientation');
    });
  }
  let reader = new FileReader();
  reader.readAsDataURL(file);
  reader.onload = function (e) {
    let image = new Image();
    image.src = this.result;
    image.onload = function () {
      var width = this.naturalWidth;
      var height = this.naturalHeight;
      // var ratio = (width < height ? width / height : height / width) / 4;
      let ratio;
      if ((ratio = width * height / 4000000)>1) {
        ratio = 1 / ratio;
      }else {
        ratio = 1;
      }

      let canvas = document.createElement("canvas");
      canvas.width = width * ratio;
      canvas.height = height * ratio;
      var ctx = canvas.getContext("2d");

      if (Orientation != "" && Orientation != 1 && Orientation !=undefined) {
        switch (Orientation) {
          case 6://需要顺时针90度旋转
            canvas.width = height * ratio;
            canvas.height = width  * ratio;
            ctx.rotate(90 * Math.PI / 180);
            ctx.drawImage(this, 0, -height * ratio, width * ratio, height * ratio);
            break;
          case 8://需要逆时针90度旋转
            canvas.width = height * ratio;
            canvas.height = width  * ratio;
            ctx.rotate(-90 * Math.PI / 180);
            ctx.drawImage(this, -width * ratio, 0, width * ratio, height * ratio);
            break;
          case 3://需要180度旋转
            ctx.rotate(180 * Math.PI / 180);
            ctx.drawImage(this, -width * ratio, -height * ratio, width * ratio, height * ratio);
            break;
          default:
            ctx.drawImage(this, 0, 0, width, height, 0, 0, width * ratio, height * ratio);
            break;
        }
      } else {
        ctx.drawImage(this, 0, 0, width, height, 0, 0, width * ratio, height * ratio);
      }

      let base64 = canvas.toDataURL("image/jpeg", 0.3);
     
    };
  };
},