title: Check if string contain only utf8 letter
body: <p>I've been searching for a method to deal with this stuff in Javascript.</p>
  
  <p>PHP has a library that handles unicode character, which called <a href="http://php.net/manual/en/regexp.reference.unicode.php" rel="nofollow">Unicode character properties</a>. Base on these patterns, UTF-8 letters can be found via something like <code>preg_match('/^\p{L}+/u', $string)</code>.</p>
  
  <p>How could I do this in JS?</p>