title: Set HTML textbox value from Javascript function return value
body: <p>I've two separate HTML file and .js file. I have a calculate method which return the result in the Javascript file. </p>
  
  <p>My question is how to set a textbox value from a Javascript return value. Or at least from a separate Javascript file. Initially I tried below which doesn't work as Javascript and html are separated.</p>
  
  <pre><code>function Calculate(ch) 
  {
      //...
      document.getElementById('Input').value = resultValue;
  }
  </code></pre>