function getListeningForDocument(mountAt) {
	  // In IE8, `mountAt` is a host object and doesn't have `hasOwnProperty`
	  // directly.
	  if (!Object.prototype.hasOwnProperty.call(mountAt, topListenersIDKey)) {
	    mountAt[topListenersIDKey] = reactTopListenersCounter++;
	    alreadyListeningTo[mountAt[topListenersIDKey]] = {};
	  }
	  return alreadyListeningTo[mountAt[topListenersIDKey]];
	}
To ensure no conflicts with other potential React instances on the page