title: Post then change text in html nodejs
body: <p>I have a form tag in Html like then:</p>
  <pre><code>app.get(&quot;/&quot;,(req,res)=&gt;{
  res.sendFile(__dirname+&quot;/index.html&quot;)
  </code></pre>
  <p>})</p>
  <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>app.post("/Cong",urlencodedParser,(req,res)=&gt;{
      var a = parseInt(req.body.a);
      var b = parseInt(req.body.b);
      var c = a + b;
      res.send("Result: "+c)//This is will route to a new website, but I just want change text in my HTML
  })</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code> &lt;form action="/Cong" method="post"&gt;
    A: &lt;input type="text" name="a"&gt;&lt;br&gt;
    B: &lt;input type="text" name="b"&gt;&lt;br&gt;
  &lt;label id="result"&gt;&lt;/label&gt;
  &lt;/form&gt;</code></pre>
  </div>
  </div>
  </p>
  <p>how I can change the label in HTML with id result = value C in file js when I click the button.</p>