Alternative to Events which got removed in Ionic 5

events.ts

import {Injectable} from '@angular/core';
import {Subject, Subscription} from 'rxjs';

/**
 * A custom Events service just like Ionic 3 Events https://ionicframework.com/docs/v3/api/util/Events/ which got removed in Ionic 5.
 *
 * @author Shashank Agrawal
 */
@Injectable({
    providedIn: 'root'
})
export class Events {

    private channels: { [key: string]: Subject<any>; } = {};

    /**
     * Subscribe to a topic and provide a single handler/observer.
     * @param topic The name of the topic to subscribe to.
     * @param observer The observer or callback function to listen when changes are published.
     *
     * @returns Subscription from which you can unsubscribe to release memory resources and to prevent memory leak.
     */
    subscribe(topic: string, observer: (_: any) => void): Subscription {
        if (!this.channels[topic]) {
            // You can also use ReplaySubject with one concequence
            this.channels[topic] = new Subject<any>();
        }

        return this.channels[topic].subscribe(observer);
    }

    /**
     * Publish some data to the subscribers of the given topic.
     * @param topic The name of the topic to emit data to.
     * @param data data in any format to pass on.
     */
    publish(topic: string, data?: any): void {
        const subject = this.channels[topic];
        if (!subject) {
            // Or you can create a new subject for future subscribers
            return;
        }

        subject.next(data);
    }

    /**
     * When you are sure that you are done with the topic and the subscribers no longer needs to listen to a particular topic, you can
     * destroy the observable of the topic using this method.
     * @param topic The name of the topic to destroy.
     */
    destroy(topic: string): null {
        const subject = this.channels[topic];
        if (!subject) {
            return;
        }

        subject.complete();
        delete this.channels[topic];
    }
}

upgrading-examples.md

1. Change the imports

Before

import {Events} from 'ionic-angular';

After

import {Events} from '../your/path/to/service/events';

2. Changes in the subscribe method

Before

events.subscribe('user:created', (user, time) => {
    console.log('Welcome', user, 'at', time);
});

After

this.events.subscribe('user:created', (data: any) => {
    console.log('Welcome', data.user, 'at', data.time);
});

3. Changes in the publish method

Before

this.events.publish('user:created', someUserInstance, Date.now());

After

this.events.publish('foo:user:logged-out', {
    user: someUserInstance,
    time: new Date()
});

4. To Unsubscribe

const subscription = this.events.subscribe('user:foo:created', (data: any) => {
    // your logic
});

Once you are done, you can do this-

subscription.unsubscribe();

Thanks! I will give it a bash!

Hi, Does someone perhaps know where I can find documentation on Unit testing this?

@grantdevon it's a Gist, a code sample; just a snippet of code, not a repo with tests, etc.
If you want unit tests, you're going to have to write them. :-)

Thanks @johnwargo for clarifying it for me.