function addEvent(node, event, fn, opt_useCapture) {
    if (typeof node.addEventListener == 'function') {
      node.addEventListener(event, fn, opt_useCapture || false)
    } else if (typeof node.attachEvent == 'function') {
      node.attachEvent('on' + event, fn)
    }
  }
Adds an event handler to a DOM node ensuring cross-browser compatibility.
@param {Node} node The DOM node to add the event handler to.
@param {string} event The event name.
@param {Function} fn The event handler to add.
@param {boolean} opt_useCapture Optionally adds the even to the capture
    phase. Note: this only works in modern browsers.