base64轉檔案（blob）遇到的一個問題

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

在Google後，仍然不能解決，~~o(>_<)o ~~

後來在看atob和btoa的demo時發現base64字串僅僅是後面的亂七八糟字串好嗎，沒有前面的名片。

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 //看這裡！！！！
Decoded String: Hello World!

而圖片的base64是這樣的：

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

所以只要後面的就可以了：

b64Data.substring(b64Data.indexOf(',') + 1)

base64轉換blob函式

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;

      };