Chain of Responsibility

An advanced way to organize your actions is using the "Chain of Responsibility". This enables you to prioritize your actions explicitly by the order of the actions.

Considering a customer service bot app with three very different layers: RuleBased layer, MachineLearning layer and HumanAgent layer, generally speaking, you may want to put the cheapest layer on the top of the chain:

const { chain } = require('bottender');

function RuleBased(context, props) {
  if (context.event.text === 'hi') {
    // discontinue and return SayHi
    return SayHi;
  }
  // continue to next
  return props.next;
}

function MachineLearningBased(context, props) {
  /* ...skip */
}

function HumanAgent(context, props) {
  /* ...skip */
}

function App() {
  return chain([
    // will execute in following order
    RuleBased,
    MachineLearningBased,
    HumanAgent,
  ]);
}

If the bot receives hi as input in the RuleBased layer, it returns SayHi and exits this chain. Otherwise, it follows the chain and goes to the MachineLearningBased layer.

chain accepts an array of actions and returns an action as return value, so it's possible to work with any pattern that compatible with actions.

Using with Router

This pattern can be used with the routing mechanism we provided and mentioned in previous section.

function RuleBased(context, { next }) {
  return router([
    text('hi', SayHi), // return SayHi when receiving hi text message
    route('*', next), // return next
  ]);
}

function App() {
  return chain([
    // will execute in following order
    RuleBased,
    MachineLearningBased,
    HumanAgent,
  ]);
}