JavaScript Code Challenge: make your own custom Emitter! (Note: you need to have Node >= 6.4.0)

README.md

JavaScript Interview Test

Fork this gist and submit a link with your solution

Usage

First, install globally expect (you need it to test your code):

npm install -global expect

Then, whenever you are done, simply do the following to know if you passed (or failed):

$ node ./test.js

FIRST STEP

Create an event emitter that goes like this:

const emitter = new Emitter();

Its instance allows you to subscribe to some event by passing a callback function

emitter.subscribe('myEvent', firstArgument => console.log('a callback!'));

...any times you want...

emitter.subscribe('myEvent', (firstArgument, secondArgument) => console.log('another callback!'));

You can emit the event you want and pass any number of arguments

emitter.emit('myEvent', 'firstArgument', 'secondArgument');

SECOND STEP

Make the return from the subscribe method to return a function that allows you to release that subscription:

const sub1 = emitter.subscribe('myEvent', () => console.log('a callback!'));
sub1();

...but all other subscriptions shall remain intact

THIRD STEP

Make the emit method return an array with every return value for each subscription callback

---

Good luck! 💪🏼💪🏼💪🏼

Emitter.js

class Emitter {
  constructor() { }
}

module.exports = Emitter

test.js

const expect = require('expect');

const Emitter = require('./Emitter');

// Step 1

let test = 0;

const emitter = new Emitter();

emitter.emit('sum', 1); // should trigger nothing

expect(test).toBe(0);

const sub1 = emitter.subscribe('sum', num => test = test + num);

emitter.emit('sum', 1); // should trigger 1 callback

expect(test).toBe(1);

const sub2 = emitter.subscribe('sum', num => test = test * num);

emitter.emit('sum', 2); // should trigger 2 callbacks

expect(test).toBe(6);

// Step 2

sub1();

emitter.emit('sum', 3); // should trigger 1 callback

expect(test).toBe(18);

// Step 3

const myEvent1 = emitter.subscribe('myEvent', () => 1);
const myEvent2 = emitter.subscribe('myEvent', () => 2);
const myEvent3 = emitter.subscribe('myEvent', () => true);
const result = emitter.emit('myEvent');

expect(result).toEqual([1, 2, true]);

console.info('You passed the test!!! 👏🏼 👏🏼 👏🏼');

I'd still rather prefer to make an npm install of local dependencies than a global npm install of a package :P

That is because you are such a hipster 😜