<div class="expandingArea">
	  <pre><span></span><br></pre>
	  <textarea></textarea>
	</div>

	<style type="text/css">
	textarea, 
	pre {
	  margin: 0;
	  padding: 0;
	  outline: 0;
	  border: 0;
	}
	
	.expandingArea {
	  position: relative;
	  border: 1px solid #888;
	  background: #fff;
	}
	
	.expandingArea > textarea,
	.expandingArea > pre {
	  padding: 5px;
	  background: transparent;
	  font: 400 13px/16px helvetica, arial, sans-serif;
	  /* Make the text soft-wrap */
	  white-space: pre-wrap;
	  word-wrap: break-word;
	}
	.expandingArea > textarea {
	  /* The border-box box model is used to allow
	   * padding whilst still keeping the overall width
	   * at exactly that of the containing element.
	   */
	  -webkit-box-sizing: border-box;
	     -moz-box-sizing: border-box;
	      -ms-box-sizing: border-box;
	          box-sizing: border-box;
	  width: 100%;
	  /* This height is used when JS is disabled */
	  height: 100px;
	}
	.expandingArea.active > textarea {
	  /* Hide any scrollbars */
	  overflow: hidden;
	  position: absolute;
	  top: 0;
	  left: 0;
	  height: 100%;
	  /* Remove WebKit user-resize widget */
	  resize: none;
	}
	.expandingArea > pre {
	  display: none;
	}
	.expandingArea.active > pre {
	  display: block;
	  /* Hide the text; just using it for sizing */
	  visibility: hidden;
	}
	</style>

	<script type="text/javascript">
	function makeExpandingArea(container) {
	 var area = container.querySelector('textarea');
	 var span = container.querySelector('span');
	 if (area.addEventListener) {
	   area.addEventListener('input', function() {
	     span.textContent = area.value;
	   }, false);
	   span.textContent = area.value;
	 } else if (area.attachEvent) {
	   // IE8 compatibility
	   area.attachEvent('onpropertychange', function() {
	     span.innerText = area.value;
	   });
	   span.innerText = area.value;
	 }
	 // Enable extra CSS
	 container.className += ' active';
	}

	var areas = document.querySelectorAll('.expandingArea');
	var l = areas.length;

	while (l--) {
	 makeExpandingArea(areas[l]);
	}
	</script>

늘어나는 Textarea

JavaScript