Github Copilot passed the Facebook EventEmitter JavaScript test... Yikes!

event-emitter-copilot.js

/**
 *
 * Create an event emitter that goes like this:
 *
    ```javascript
    const emitter = new Emitter();
    ```

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

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

    ...any times you want...

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

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

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

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

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

    ...but all other subscriptions shall remain intact.

    * Make the emit method return an array with every return value for each subscription callback.
*/
export default class EventEmitter {
    constructor() {
        this.subscriptions = {};
    }
    subscribe(event, callback) {
        if (!this.subscriptions[event]) {
            this.subscriptions[event] = [];
        }
        this.subscriptions[event].push(callback);
        return () => {
            const index = this.subscriptions[event].indexOf(callback);
            this.subscriptions[event].splice(index, 1);
        };
    }
    emit(event, ...args) {
        if (!this.subscriptions[event]) {
            return [];
        }
        return this.subscriptions[event].map((subscription) =>
            subscription(...args)
        );
    }
}