Using Async/Await in WATSON Nodejs SDK

Question

I am building a chatbot with WATSON API where I use the async/await method in order to fetch the data from MongoDB and attain the result, which then I send it back to the user.

The function artpromise is the promise that collects data from mongo DB. And the function randomartist is a function that fetches 3 random document from the DB. However, the WATSON BLUEMIX Cloud service supports Nodejs SDK of 6.1.3 which does not support the async method. Is there any way to update the SDK version on Blumix or should I use a difference approach in fetching data from the server?

let getConversationResponse = (message, context) => {
  let payload = {
    workspace_id: process.env.WORKSPACE_ID,
    context: context || {},
    input: message || {}
  };

  payload = preProcess(payload);

  return new Promise((resolved, rejected) => {
    // Send the input to the conversation service
    conversation.message(payload, async function(err, data) {
      if (err) {
        rejected(err);
      }
      else{
          if(data.context.type == 'ask'){
              let artist = data.context.name;
              let result = await artpromise(artist);
              console.log(result);
              data.context.name  = result[0].name;
              data.context.nationality = result[0].nationality;
              data.context.birth = result[0].years;
              data.context.url = result[0].art_link;
              data.output.text = data.context.name+' is a '+data.context.nationality+' artist  from '+data.context.birth+'. Check out a painting at '+data.context.url;
          }

          else if(data.context.type == 'random_artist'){
              let result = await randomArtist();
              console.log(result);
              data.output.text = 'Let\'s find some random artists for you! \n'+result;
          }
        let processed = postProcess(data);
        if(processed){
          // return 값이 Promise 일 경우
          if(typeof processed.then === 'function'){
            processed.then(data => {
              resolved(data);
            }).catch(err => {
              rejected(err);
            })
          }
          // return 값이 변경된 data일 경우
          else{
            resolved(processed);
          }
        }
        else{
          // return 값이 없을 경우
          resolved(data);
        }
      }
    });
  })
} 

Answer 1

Using Node's util.promisify() utility, you can transform a callback-style function into a Promise-based one.

Somewhere outside of your getConversationResponse-function, assign it to a local variable:

const util = require('util');
const messagePromise = util.promisify(conversation.message);

And use that function instead. Something like this should work:

const util = require('util');
const messagePromise = util.promisify(conversation.message);

let getConversationResponse = async (message, context) => {
  let payload = preprocess({
    workspace_id: process.env.WORKSPACE_ID,
    context: context || {},
    input: message || {}
  });

  let data = await messagePromise(payload);
  if (data.context.type == 'ask') {
    let artist = data.context.name;
    let result = await artpromise(artist);
    console.log(result)
    data.context.name  = result[0].name;
    data.context.nationality = result[0].nationality;
    data.context.birth = result[0].years;
    data.context.url = result[0].art_link;
    data.output.text = data.context.name+' is a '+data.context.nationality+' artist  from '+data.context.birth+'. Check out a painting at '+data.context.url;
  } else if (data.context.type == 'random_artist'){
    let result = await randomArtist();
    console.log(result);
    data.output.text = 'Let\'s find some random artists for you! \n'+result;
  }

  return postProcess(data) || data;
};

Note that if the return value of postProcess is falsy, it will return the data variable instead. Additionally, an async function always returns a Promise, so to call this function, you'll do:

getConversationResponse(message, context).then((data) => {
  // Do something with the data
}).catch((e) => {
  // Handle the error!
});

or if you call it from another async function:

let data = await getConversationResponse(message, context);

or if you need to specifically catch errors in the calling async function:

try {
  let data = await getConversationResponse(message, context);
} catch (e) {
  // Handle error
}

Just like regular synchronous code, any error thrown in the function call chain "trickles up" to the top-most callee. If you're confused about this, I suggest reading up on error handling.

If you want to use the Watson API in an async Promise-based fashion throughout your code, it might be feasible to write a small wrapper library and use that directly instead.

---

A Promise-only implementation:

const util = require('util');
const messagePromise = util.promisify(conversation.message);

let getConversationResponse = (message, context) => {
  let payload = preprocess({
    workspace_id: process.env.WORKSPACE_ID,
    context: context || {},
    input: message || {}
  });

  return messagePromise(payload).then((data) => {
    if (data.context.type == 'ask') {
      let artist = data.context.name;
      return artpromise(artist).then((result) => {
        data.context.name  = result[0].name;
        data.context.nationality = result[0].nationality;
        data.context.birth = result[0].years;
        data.context.url = result[0].art_link;
        data.output.text = data.context.name+' is a '+data.context.nationality+' artist  from '+data.context.birth+'. Check out a painting at '+data.context.url;
        return data;
      });
    } else if (data.context.type == 'random_artist') {
      return randomArtist().then((result) => {
        data.output.text = 'Let\'s find some random artists for you! \n' + result;
        return data;
      });
    }
  }).then((data) => {
    return postProcess(data) || data;
  });
};

Calling it is the exact same as the async/await implementation.