html5-data.js

(function () {  
  function detectMutation() {
    mutationSupported = true;
    this.removeEventListener('DOMAttrModified', detectMutation, false);
  }

  var forEach = [].forEach, 
      regex = /^data-(.+)/,
      el = document.createElement('div'),
      mutationSupported = false;

  el.addEventListener('DOMAttrModified', detectMutation, false);
  el.setAttribute('foo', 'bar');

  Element.prototype._datalistCache = {};
  Element.prototype._datalistCacheValid = false;
  Element.prototype.__defineGetter__('datalist', function () {
    var i = this.attributes.length, match, el = this;
    if (!mutationSupported || !this._datalistCacheValid) {
      this._datalistCacheValid = true;
      forEach.call(this.attributes, function(attr) {
        if (match = attr.name.match(regex))
          el._datalistCache[match[1]] = attr.value;
      });
    }
    return this._datalistCache;
  });

  document.body.addEventListener('DOMAttrModified', function (event) {
    event.target._datalistCacheValid = false;
  }, false);
})();