Textarea autogrow

autogrow.js

function autogrow(textarea) {
	
	// create fake div with same content
	// (only works with box-sizing border-box)
	var dv = document.createElement("div");
	dv.className = 'fm-growable';
	dv.style.visibility="hidden";
	dv.style.position="absolute";
	textarea.parentNode.appendChild(dv);
	
	function resize() {
		// copy current textarea content
		dv.style.width = textarea.offsetWidth + 'px';
		dv.innerHTML   = textarea.value.replace(/\r\n|\n/g, "<br>");
		dv.innerHTML  += textarea.value[textarea.value.length-1] === '\n'? 'A' : ''; // trailing char if ends in \n
	    
	    // set textarea size to be the same as the div
	    textarea.style.height = dv.offsetHeight + "px";
	}
	
	// resize right way if has some initial content
	resize();
	
	// resize onkeydown
	textarea.addEventListener('keydown', resize, false);
	textarea.addEventListener('input', resize, false);
	textarea.addEventListener('propertychange', resize, false);
}