title: Send arrayBuffer with body
body: <p>I'm trying to use the file reader api and send data to a server. I've so far found out that I can't use readAsBinaryString anymore (it's been deprecated) but instead have to use readAsArrayBuffer.</p>
  
  <p>I also have to send a body with the request. So my initial request looked like this:</p>
  
  <pre><code>var binaryString= fileData; //populated earlier from readAsBinaryString()
  
  var body = "";
  body += ...
  body += binaryString;
  
  xhr.open("POST", url, true);
  xhr.setRequestHeader("Content-Type", "multipart/form-data;...");
  xhr.send();
  </code></pre>
  
  <p>I can't seem to use this when doing an arrayBuffer. I've tried converting the arrayBuffer to a string but that's too memory intensive for large files. So my question is how do I send arrayBuffer data AND a body at the same time.</p>