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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

              
                <main>
  <h2>Textarea Auto-Resize with JavaScript</h2>
  
  <textarea placeholder="Type many lines of texts in here and you will see magic stuff" class="txta"></textarea>
  
  <!-- Uncomment this to see multiple textareas in action -->
  <!-- <textarea placeholder="Type many lines of texts in here and you will see magic stuff" class="txta common"></textarea>-->

</main>
              
            
!

CSS

              
                body {
  font-family: Arial, sans-serif;
  padding: 0 20px;
}

h2 {
  font-size: 30px;
}

main {
  text-align: center;
  margin: 0 auto;
  max-width: 800px;
}

textarea {
  color: #444;
  padding: 5px;
}

/* TEXTAREA AUTO RESIZE STYLES BEGIN */

/* The .hiddendiv styles are added with JS.
   You can remove the JS lines and use CSS instead
.hiddendiv {
  display: none;
  white-space: pre-wrap;
  word-wrap: break-word;
}*/

/* the styles for 'txta' are applied to both the textarea and the hidden clone */
/* these must be the same for both */
.txta {
  width: 100%;
  max-width: 500px;
  min-height: 100px;
  font-family: Arial, sans-serif;
  font-size: 16px;
  overflow: hidden;
  line-height: 1.4;
}
/* TEXTAREA AUTO RESIZE STYLES END */
              
            
!

JS

              
                // Targets all textareas with class "txta"
let textareas = document.querySelectorAll('.txta'),
    hiddenDiv = document.createElement('div'),
    content = null;

// Adds a class to all textareas
for (let j of textareas) {
  j.classList.add('txtstuff');
}

// Build the hidden div's attributes

// The line below is needed if you move the style lines to CSS
// hiddenDiv.classList.add('hiddendiv');

// Add the "txta" styles, which are common to both textarea and hiddendiv
// If you want, you can remove those from CSS and add them via JS
hiddenDiv.classList.add('txta');

// Add the styles for the hidden div
// These can be in the CSS, just remove these three lines and uncomment the CSS
hiddenDiv.style.display = 'none';
hiddenDiv.style.whiteSpace = 'pre-wrap';
hiddenDiv.style.wordWrap = 'break-word';

// Loop through all the textareas and add the event listener
for(let i of textareas) {
  (function(i) {
    // Note: Use 'keyup' instead of 'input'
    // if you want older IE support
    i.addEventListener('input', function() {
      
      // Append hiddendiv to parent of textarea, so the size is correct
      i.parentNode.appendChild(hiddenDiv);
      
      // Remove this if you want the user to be able to resize it in modern browsers
      i.style.resize = 'none';
      
      // This removes scrollbars
      i.style.overflow = 'hidden';

      // Every input/change, grab the content
      content = i.value;

      // Add the same content to the hidden div
      
      // This is for old IE
      content = content.replace(/\n/g, '<br>');
      
      // The <br ..> part is for old IE
      // This also fixes the jumpy way the textarea grows if line-height isn't included
      hiddenDiv.innerHTML = content + '<br style="line-height: 3px;">';

      // Briefly make the hidden div block but invisible
      // This is in order to read the height
      hiddenDiv.style.visibility = 'hidden';
      hiddenDiv.style.display = 'block';
      i.style.height = hiddenDiv.offsetHeight + 'px';

      // Make the hidden div display:none again
      hiddenDiv.style.visibility = 'visible';
      hiddenDiv.style.display = 'none';
    });
  })(i);
}
              
            
!
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