Angular Services Polling

This project represents a Proof of Concept about realizing a centralized Polling service, in Angular 2+, by using Reactive Programming tools (RxJS - https://rxjs-dev.firebaseapp.com/).

Scenario

The scenario I tried to simulate is the following:

We have a principal /services endpoint which provides information about several services (e.g. notifications, appointments). This endpoint maps each business service to a proper version number, which is used to evaluate if we need to update its business service content, by downloading that information from a dedicated REST endpoint.

For example, after X seconds, /services endpoint returns a bigger version for the notifications service. Immediately, the /notifications endpoint gets called, and new notifications are retrieved and showed by the related angular component.

Exposing mocked REST APIs

Mocked APIs are exposed through JSON Server (https://github.com/typicode/json-server), a smart utility which is able to expose REST API starting from a json file.

1. Install JSON Server

   npm install -g json-server

2. From project root folder, boot it

   json-server rest-api/db.json

Running the Application

1. Install the Angular CLI

   npm install -g @angular/cli

2. Run npm install

3. Run npm start

Technical details

The angular service which is responsible to orchestrate all business services synchronization is src/app/polling/services/polling.service.ts. This TypeScript class contains the aim of an injectable service which can be invoked by two methods:

1. startPolling it enables polling (if it not yet enabled) for an input service name.
2. subscribeToPollingService for the given service name, it subscribes to each update that will be available for it (e.g. new notifications)

An example of an end angular component which is using these two methods is navbar-notifications.component.ts.