botCodeHook.js

'use strict';
exports.handler = (event, context, callback) => {
    const sessionAttributes = event.sessionAttributes;
    const slots = event.currentIntent.slots;
    const bookName = slots.bookName;
  
    // predefined list of available books
    const validBooks = ['harry potter', 'twilight', 'wings of fire'];
  
    // negative check: if valid slot value is not obtained, inform lex that user is expected 
    // respond with a slot value 
    if (bookName && !(bookName === "") && validBooks.indexOf(bookName.toLowerCase()) === -1) {
        let response = { sessionAttributes: event.sessionAttributes,
          dialogAction: {
            type: "ElicitSlot",
             message: {
               contentType: "PlainText",
               content: `We do not have book: ${bookName}, Provide any other book name. For. e.g twilight.`
            },
             intentName: event.currentIntent.name,
             slots: slots,
             slotToElicit : "bookName"
          }
        }
        callback(null, response);
    }
  
    // if valid book name is obtained, send command to choose next course of action
    let response = {sessionAttributes: sessionAttributes,
      dialogAction: {
        type: "Delegate",
        slots: event.currentIntent.slots
      }
    }
    callback(null, response);
};