code: function(stateOnDefined) {
        const onDefinitionError = (err) => {
          this.failedWith = err;
          this.transition('failed');
        };
        const onDefined = () => {
          this.transition(stateOnDefined);
        };
        this.channel.define()
          .then(onDefined, onDefinitionError);
      }
docs: Defines exchange
  
  @private
  @memberOf ExchangeMachine.prototype