docs: function() {
      var callbacks = this._callbacks;
      var contexts = this._contexts;
      if (callbacks) {
        ("production" !== process.env.NODE_ENV ? invariant(
          callbacks.length === contexts.length,
          'Mismatched list of contexts in callback queue'
        ) : invariant(callbacks.length === contexts.length));
        this._callbacks = null;
        this._contexts = null;
        for (var i = 0, l = callbacks.length; i < l; i++) {
          callbacks[i].call(contexts[i]);
        }
        callbacks.length = 0;
        contexts.length = 0;
      }
    }