text: if (!global._graceBus) {
    global._graceBus = {}
  }
  export default {
    $emit(eventName, ...arg) {
      var cbs = global._graceBus[eventName];
      for (var cb of cbs) {
        cb.apply(null, arg);
      }
    },
    $on(eventName, cb) {
      global._graceBus[eventName] = global._graceBus[eventName] || [];
      global._graceBus[eventName].push(cb);
    },
    $off(eventName, cb){
      var cbs = global._graceBus[eventName] || [];
      if (cb) {
        for (var index = 0; index < cbs.length; ++index) {
          if (cb == o) {
            cbs.splice(index, 1);
            break
          }
        }
      } else {
        global._graceBus[eventName] = [];
      }
    }
  }