在过程中，发现报错如下：

failed to execute ‘atob’ on ‘window’: the string to be decoded is not correctly encoded.

在Google后，仍然不能解决，~~o(>_<)o ~~

后来在看atob和btoa的demo时发现base64字符串仅仅是后面的乱七八糟字符串好吗，没有前面的名片。

var str = “Hello World!”;
var enc = window.btoa(str);
var dec = window.atob(enc);

var res = “Encoded String: ” + enc + “
” + “Decoded String: ” + dec;

The result of res will be:

Encoded String: SGVsbG8gV29ybGQh //看这里！！！！
Decoded String: Hello World!

而图片的base64是这样的：

data:image/gif;base64,/9j/4AAQSkZJRgABAQ……..

所以只要后面的就可以了：

b64Data.substring(b64Data.indexOf(‘,’) + 1)

base64转换blob函数

function b64toBlob(b64Data, contentType, sliceSize) {

        contentType = contentType || '';

        sliceSize = sliceSize || 512;



        var byteCharacters = atob(b64Data.substring(b64Data.indexOf(',') + 1));

        var byteArrays = [];



        for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {

          var slice = byteCharacters.slice(offset, offset + sliceSize);



          var byteNumbers = new Array(slice.length);

          for (var i = 0; i < slice.length; i++) {

            byteNumbers[i] = slice.charCodeAt(i);

          }



          var byteArray = new Uint8Array(byteNumbers);



          byteArrays.push(byteArray);

        }



        var blob = new Blob(byteArrays, {type: contentType});

        return blob;

      };