title: how can I update a shiny fileInput object?
body: <p>I want to create an input file dialog. This is straightforward using the <code>fileInput</code> function. </p>
  
  <pre><code>shinyUI(pageWithSidebar(
    headerPanel(""),
    sidebarPanel(
      fileInput("file", "Select a file")  
    ),
    mainPanel()
  ))
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/2l6w2.png" alt="enter image description here"></p>
  
  <p>After uploading it looks like this:
  <img src="https://i.stack.imgur.com/9b2lT.png" alt="enter image description here"></p>
  
  <p>Now, I want to reset the <code>inputFile</code> element to the state it had before uploading. As there is no such function like <code>updateFileInput</code>, me being a JS/HTML rookie, I am not able to figure out how I could achieve that. The code output from <code>fileInput("file", "Select a file")</code> is the following.</p>
  
  <pre><code>&lt;label&gt;Select a file&lt;/label&gt;
  &lt;input id="file" type="file" accept="text/plain"/&gt;
  &lt;div id="file_progress" class="progress progress-striped active shiny-file-input-progress"&gt;
    &lt;div class="bar"&gt;&lt;/div&gt;
    &lt;label&gt;&lt;/label&gt;
  &lt;/div&gt; 
  </code></pre>
  
  <p>Any ideas?</p>
  
  <p>PS. I do not want to use a reactive <code>renderUI</code> here to re-render the file input element. I'd rather want to go the 'update way' (if there is such a thing) ...</p>