Textarea auto-resize vanilla javascript (no jQuery plugin), for modern browsers

;(function () {
  function domReady (f) { /in/.test(document.readyState) ? setTimeout(domReady,16,f) : f() }

  function resize (event) {
    event.target.style.height = 'auto';
    event.target.style.height = event.target.scrollHeight+'px';
  }
  /* 0-timeout to get the already changed text */
  function delayedResize (event) {
    window.setTimeout(resize, 0, event);
  }

  domReady(function () {
    var textareas = document.querySelectorAll('textarea[auto-resize]')

    for (var i = 0, l = textareas.length; i < l; ++i) {
      var el = textareas.item(i)

      el.addEventListener('change',  resize, false);
      el.addEventListener('cut',     delayedResize, false);
      el.addEventListener('paste',   delayedResize, false);
      el.addEventListener('drop',    delayedResize, false);
      el.addEventListener('keydown', delayedResize, false);
    }
  })
}());


// Use: <textarea auto-resize></textarea>