title: Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'
body: <p>I have an uploader that allows a user to upload several pictures. In order to only create or update the images he wants to add/change, I update an object that looks like this:</p>
  <p><code>{main: Blob, &quot;1&quot;: Blob, &quot;2&quot;:Blob}</code></p>
  <p>So if only needs to update &quot;1&quot; later, the sent object will only contain
  <code>{&quot;1&quot;: Blob}</code></p>
  <p>When clicking on save, it triggers a function that is supposed to append the images to a formData(). Sadly the formData is never updated. I have the following error:</p>
  <blockquote>
  <p>Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'.</p>
  </blockquote>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>export async function uploadImages(files, userId) {
    try {
      const images = new FormData();
      files.main &amp;&amp; images.append("image", files.main, "main");
      files[1] &amp;&amp; images.append("image", files[1], "1");
      files[2] &amp;&amp; images.append("image", files[2], "2");
  
      const res = await ax.post(process.env.SERVER_URL + "/upload-images", {
        images,
        userId,
      });
      return "success"
    } catch (err) {
      return "error"
    }
  }</code></pre>
  </div>
  </div>
  </p>
  <p>How to fix this? Thanks!</p>