Скачать или смотреть Efficiently Add a Polling Mechanism to HTTP Calls in Angular 8

Learn how to implement a `polling mechanism` for HTTP calls in Angular 8 to retrieve job status every minute efficiently.
---
This video is based on the question https://stackoverflow.com/q/62517694/ asked by the user 'Ana' ( https://stackoverflow.com/u/13066398/ ) and on the answer https://stackoverflow.com/a/62518352/ provided by the user 'bharat1226' ( https://stackoverflow.com/u/4898346/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Adding polling mechanism to a http call in Angular 8

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Efficiently Add a Polling Mechanism to HTTP Calls in Angular 8

In modern web applications, it's common to need real-time or near-real-time data updates. One effective way to achieve this is through a polling mechanism—a strategy for regularly checking for updates from a server. In this guide, we will dive into how to implement a polling mechanism for an HTTP call in an Angular 8 application.

The Problem: Requesting Job Status Multiple Times

Suppose you have a service designed to request information about a job's status based on a given JOB_ID. The basic requirement is to fetch this status every minute to keep your application’s data up-to-date.

Initial Implementation

Here’s how the original HTTP request looks:

[[See Video to Reveal this Text or Code Snippet]]

While the above code correctly fetches data from the server, it only executes once. To ensure that we constantly receive updates, we need to add a polling mechanism.

The Solution: Adding Polling with RxJS

Using Observables with Timers

To implement the polling mechanism, we can use RxJS, a library for reactive programming in JavaScript that Angular heavily relies on. The timer function enables us to create an observable that emits a value after a specified duration, and we can repeat this process to achieve our polling.

Here’s how to modify the existing method to include polling:

[[See Video to Reveal this Text or Code Snippet]]

Breaking Down the Code

timer(0, 60000): This line initializes the timer to emit immediately (0 milliseconds), and then every 60000 milliseconds (or one minute).

switchMap: This operator is crucial as it cancels any previous subscription to the observable when a new value is emitted. This way, if a new request is made before the previous one completes, it will switch to a new observable and discard the previous one.

http.get Status (url): This continues to fetch the job status from the provided URL every minute.

Benefits of Polling

Real-time Updates: Your application will always have the latest job status without any manual refresh.

Improved User Experience: Users won't need to worry about refreshing the page to get updated information.

Considerations

While polling can be highly effective, keep in mind the possible drawbacks:

Network Load: Constant requests can increase the load on both your server and user’s network, so it’s essential to balance how often you poll.

Delay in Updates: Depending on your polling interval, there may be slight delays in receiving the latest data.

Conclusion

By implementing a polling mechanism in Angular 8 using RxJS, you can easily keep your application updated with the latest information from the server. This approach is efficient, user-friendly, and straightforward. As you continue to build your Angular applications, consider utilizing polling where real-time updates are necessary!

Feel free to ask any questions or share your experiences implementing polling in Angular applications in the comments below!