infinite interactivity with Inquirer.js

intro: …do what with Inquirer?

Last weekend I spent some time on a silly side project, and I was working towards a minimum, proof-of-concept “port” of the famous¹ Rogerian therapist chatbot “Eliza” into the generator-based chatbot framework I had already started putting together. I didn’t yet have any user input functionality in the UI for the project, so I wanted to test out my port in the simplest way possible: via interactive command line.

I’ve used commander before for making Node CLI tools, but I knew it wouldn’t provide the interactivity I was looking for—namely, being able to input text and test an Eliza instance’s responses, back-and-forth, indefinitely. So I went looking around for other Node CLI libraries and soon came across Inquirer, which looked like it might fit the bill.

Spoiler: it did…eventually.

Read on for a short story of hacking an interactive question/answer CLI library into a chatbot framework, including a tiny taste of RxJS (😮!).

prerequisites

This blog post assumes a moderate familiarity with:

• JavaScript/Node.js
• command-line interface (CLI) tools
• some ES2015 features:
  • arrow functions
  • destructuring assignment
  • template literals

If you’re interested in the material here but need help with some of these assumed concepts, please reach out to me, and I’ll try my best to help!

Inquirer basics

After installing Inquirer with npm install inquirer, you can get up and running very quickly. A tool that asks the user to input their name and then choose their favorite from a list of ice cream flavors take only about 14 lines of code:

💣 NB: One thing that tripped me up initially with Inquirer was that fact that the examples I found from older blog posts employed a callback in the second argument to inquirer.prompt to retrieve the answers. Since full support for Promises came into Node with version 4.x+, inquirer.prompt([questions]) has been updated to return a Promise.

adding infinite interactivity with RxJS

In order to use Inquirer for the ✨∞ infinite ∞✨ back-and-forth interactivity that you need to have an open-ended conversation with a chatbot, you need to be able to dynamically add new prompts. Since Inquirer already uses RxJS under the hood, you can use RxJS in your Node script to achieve infinite interactivity.

Start by installing the same version of RxJS that Inquirer depends on—as of this writing, that’s rx 4.x², so npm install rx.

Then after requireing Rx in addition to Inquirer, we can create a Subject:

const inquirer = require('inquirer');
const Rx = require('rx');

const prompts = new Rx.Subject();

Instead of initializing inquirer.prompt with an array of JavaScript objects, each encoding a question to be asked the user, we instead pass inquirer.prompt the new Rx Subject constant prompts we’ve just created. Then we access the callbacks we’ll need for a reactive interface with ui.process.subscribe:

inquirer.prompt(prompts).ui.process.subscribe(
 onEachAnswer,
 onError,
 onCompleted,
);

The onEachAnswer callback receives an object representing the answer with two properties: name (= the name property in the prompt) and answer (= the user’s input). It’s in the onEachAnswer callback that we have the opportunity to dynamically create a new prompt and surface it in the user’s current session using the Rx Subject’s onNext function:

// onEachAnswer callback
({ answer }) => {
 prompts.onNext(makePrompt(`This is prompt \#${i}.`));
}

To create each question/prompt, we can define a simple makePrompt function:

function makePrompt(msg) {
 return {
   type: 'input',
   name: `userInput-${i}`,
   message: `${msg || 'Say something to start chatting!'}\n\n`,
 };
}

We kick off the chat with a simple call to prompts.onNext (passing in the default prompt resulting from makePrompt()) at the end of the file: prompts.onNext(makePrompt()).

Altogether, the simplest infinitely interactive Inquirer script with dynamically generated prompts looks something like this: