Base64转Blob对象

function base64ToBlob(base64){
  var base64Split = base64.split(',');
  var binStr = atob( base64Split[1] ),
  len = binStr.length,
  arr = new Uint8Array(len);

  for (var i=0; i<len; i++ ) {
    arr[i] = binStr.charCodeAt(i);
  }
  return new Blob( [arr], {type: base64Split[0].split(':')[1]} );
}

Base64转File对象

function base64ToFile(base64, filename){
    var base64Split = base64.split(',');
    var base64Data = base64Split[1];
    var contentType = base64Split[0].split(':')[1];
    var sliceSize = 1024;
    var byteCharacters = atob(base64Data);
    var bytesLength = byteCharacters.length;
    var slicesCount = Math.ceil(bytesLength / sliceSize);
    var byteArrays = new Array(slicesCount);

    for (var sliceIndex = 0; sliceIndex < slicesCount; ++sliceIndex) {
        var begin = sliceIndex * sliceSize;
        var end = Math.min(begin + sliceSize, bytesLength);

        var bytes = new Array(end - begin);
        for (var offset = begin, i = 0 ; offset < end; ++i, ++offset) {
            bytes[i] = byteCharacters[offset].charCodeAt(0);
        }
        byteArrays[sliceIndex] = new Uint8Array(bytes);
    }
    return new File(byteArrays, filename, { type: contentType });
}

Blob对象转成File对象

function blobToFile( blob, filename) {
    return new File([ blob ], filename, {type: blob.type});
}