title: html image blob to base64
body: <p>I've got some problems about to fileinputjs.The  images' src  are blob.But i want to use images' src to do something.So i use readAsDataURL to get base64.But there are any problems about it 。</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
       $("#last").click(function(){
         var blob=document.querySelector(".file-preview-image").src;
         var reader = new FileReader(); //通过 FileReader 读取blob类型
     reader.onload = function(){
      this.result === dataURI; //base64编码
      }
      console.log(reader.readAsDataURL(blob));
  })
       &lt;/script&gt;
  </code></pre>
  
  <p>Then there are <code>Uncaught TypeError: Failed to execute 'readAsDataURL' on 'FileReader': parameter 1 is not of type 'Blob'</code>.</p>