var bind, unbind, prefix;

function detect () {
  bind = window.addEventListener ? 'addEventListener' : 'attachEvent';
  unbind = window.removeEventListener ? 'removeEventListener' : 'detachEvent';
  prefix = bind !== 'addEventListener' ? 'on' : '';
}

/**
 * Bind `el` event `type` to `fn`.
 *
 * @param {Element} el
 * @param {String} type
 * @param {Function} fn
 * @param {Boolean} capture
 * @return {Function}
 * @api public
 */

exports.bind = function(el, type, fn, capture){
  if (!bind) detect();
  el[bind](prefix + type, fn, capture || false);
  return fn;
};

/**
 * Unbind `el` event `type`'s callback `fn`.
 *
 * @param {Element} el
 * @param {String} type
 * @param {Function} fn
 * @param {Boolean} capture
 * @return {Function}
 * @api public
 */

exports.unbind = function(el, type, fn, capture){
  if (!unbind) detect();
  el[unbind](prefix + type, fn, capture || false);
  return fn;
};