Resizeable Textbox

HTML script
        
<html>
<head></head>
<body>

<form method="POST" action="" enctype="multipart/form-data">
    <textarea rows="4" name="text" placeholder="Cambridge is a mental hospital." style="width:50%"></textarea>
    <button type="submit" name="submit_form_button" >Submit</button>
    <div id="filetext">
    </div>
</form>

<script>
  var textarea = document.querySelector('textarea');

  textarea.addEventListener('keydown', autosize);

  function autosize(){
    var el = this;
    setTimeout(function(){
      el.style.cssText = 'height:auto; padding:0';
      // for box-sizing other than "content-box" use:
      // el.style.cssText = '-moz-box-sizing:content-box';
      el.style.cssText = 'height:' + el.scrollHeight + 'px';
    },0);
  }
</script>
</body>
</html>
Resizeable Textbox

References
