title: Is it possible to replace a file input with a Blob?
body: <p>I am working with an online application of which I do not have access to the source, but I am able to inject javascript on it via iframe because I can create pages in the same domain.</p>
  
  <p>This application has a form it submits for file upload, and file inputs, think:</p>
  
  <pre><code>&lt;form&gt;
     &lt;!-- lots and lots of inputs --&gt;
     &lt;input type="file" name="blah"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>I would like to use this form to submit a javascript Blob for this particular file instead of a file from disk, while not disturbing the rest of the form. How do I do this?</p>