JavaScript - contenteditable Empty or WhiteSpaces
HTML
<div id="message" contenteditable="true">Digite sua mensagem</div>
JavaScript
$(function() {
var $target = $('#message');
$target.on("keyup", function() {
var value = $target.text();
if (value.length === 0 || !value.trim())
return false;
// continue...
alert(value);
});
});