KdWbWE

index.html

<textarea rows="1"></textarea>

KdWbWE.markdown

KdWbWE

A Pen by Captain Anonymous on CodePen.

License.

script.js

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);
}

scripts

<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>

style.css

textarea {
  /*position: absolute;*/
  border: none;
  /*min-width: 50%;*/
  
  font-size: 20px;
  line-height: 28px;
  
  padding: 25px;
  
  width: 80%;
  display: block;
  margin-top: 15px;
  margin-left: auto;
  margin-right: auto;
  resize: none;
  overflow: hidden;
}

textarea:focus {
  outline: none;
}