Table of content

For this purpose, the RxJS library (Reactive Extensions) is used to help you manage asynchronous data and events. This library has a complex syntax, but our little guide will help you get to grips with it in a fairly simple way.

Introduction

The RxJS library has a number of powerful operators for performing various transformations, filtering and merging data streams. Debugging with RxJS — the most intricate library in the Angular web development ecosystem — will enhance your understanding of data flow.

RxJS data streams can cause problems in various ways:

  • Wrong order of execution. The code is not executed in the expected order.
  • Data loss. Some events do not reach the subscriber.
  • Memory leaks. Subscriptions are not closed, resulting in excessive load.
  • Silent errors. Streaming exceptions are not visible without explicit error handling.

You should start troubleshooting by clearly understanding where in the code the problem occurs: it could be where an observable is created, a data transformation (such as map or switchMap), or a subscription. Understanding services in angular can also be crucial in this process, as they often manage data flow.

1. Creating Services in Angular

To use angular create service, you can generate a service using the Angular CLI. Services are crucial for encapsulating business logic and data management, allowing components to remain focused on the UI.

ng generate service my-service

2.  Using console logging

For simple checks, add console.log to the tap statement or at the time of subscription:

typescript 

import { of } from ‘rxjs’;

import { tap, map } from ‘rxjs/operators’;

of(1, 2, 3).pipe(

  tap(value => console.log(‘Before the transformation:’, value)),

  map(value => value  2),

  tap(value => console.log(‘After the transformation:’, value))

).subscribe();

Tap is ideal for seeing what happens within an observable chain. With this operator, you can log intermediate data without changing the flow, which helps you to track the order of execution and detect errors. The placement of console.log within tap shows what data passes through each step. This is useful to check if the transformations are correct and to look for inconsistencies. Leveraging angular services here can provide additional context and control.

3. Using DevTools to debug asynchronous code

When you need to debug angular application effectively, there are several strategies you can employ:

  • Console Logging: Use console.log() to track variable values and execution flow.
  • Angular DevTools: This browser extension provides insights into change detection and component hierarchy.

How to debug angular in Chrome? Modern browsers support debugging of asynchronous calls. To do this:

  1. Open Chrome DevTools (or a similar tool).
  2. Search for the desired file in the “Sources” tab.
  3. Add a breakpoint within the stream where a subscription or data processing is being performed.
  4. Use Call Stack to understand the sequence of operator calls.

DevTools allows you to set breakpoints at asynchronous code execution points such as subscriptions and event handlers. This allows you to monitor thread execution step-by-step and detect errors in the call order, when events are triggered and what data is passed between statements. Using vscode angular debug can also be beneficial in identifying issues in your code.

By mastering these tools and techniques, you can efficiently debug in angular and enhance your application’s stability and performance.

4. RxJS DevTools

RxJS DevTools is a browser extension (available for Chrome and Firefox) that greatly simplifies the debugging and visualization of RxJS threads. You can use it to monitor observables, check which operators are being used, see errors and find memory leaks. Learn how to work with this tool here.

RxJS DevTools is a browser extension that visualizes the operation of RxJS threads. It helps you to keep track of instructions, subscripts and transferred data, which makes troubleshooting and finding problems such as memory leaks or incorrect subscripts much easier.

Installation and customization

  1. Install the extension via the browser store:
    • Chrome: Chrome Web Store
    • Firefox: Firefox Add-ons
  2. Make sure that the project uses RxJS version 6+.
  3. Run the application in development mode so that the extension can collect data from Observable.

Thread Visualization

RxJS DevTools displays all active threads and operator chains in real time. You can see how data flows through operators such as map, switchMap or filter. Each step is displayed in a sequence, which helps you understand which operators are called and when.

Subscription Tracking

The tool tracks all active and completed subscriptions. Uncompleted subscriptions are highlighted so you can quickly find memory leaks. This is particularly useful if your code uses long-lived threads that need to be terminated manually with operators such as takeUntil.

Event History

The extension records all exceptions and displays them together with the statements in which they occurred. For example, if an error occurs within a sequence, DevTools shows in which phase it occurred. This facilitates diagnosis and speeds up the rectification process.

Error Search

The extension captures all exceptions and displays them along with the statements where they occurred. For example, if an error is thrown within a flow, DevTools will show you at which stage it occurred. This makes it easier to diagnose and speeds up the fixing process.

RxJS DevTools helps you monitor thread behavior in a structured and visual way, minimizing the time spent debugging complex reactive chains.

5. Tracking the completion of subscriptions

Memory leaks occur when an observable continues to run after a component or service angular is no longer in use. This happens if the subscription was not terminated correctly. Even if the component is destroyed, the thread continues to generate data, which consumes memory and resources. Over time, this can slow down or stop the application.

To avoid leaks, it is important to manage the lifetime of subscriptions. This is done by using operators such as takeUntil, unsubscribe or the automatic management of subscriptions via async pip in templates.

Example with takeUntil:

import { Subject, interval } from ‘rxjs’;

import { takeUntil } from ‘rxjs/operators’;

const destroy$ = new Subject();

interval(1000).pipe(

  takeUntil(destroy$)

).subscribe(value => console.log(value));

// End subscription in 5 seconds

setTimeout(() => {

  destroy$.next();

  destroy$.complete();

  console.log(‘Subscription completed’);

}, 5000);

6. Error handling in threads

In RxJS, errors in threads are not passed on automatically – if you do not add an explicit error handling statement, the thread will simply exit with an error and you will not see what went wrong. Operators such as catchError and retry are used for this purpose.

  • catchError makes it possible to catch an error and replace it with alternative data or perform necessary actions (e.g. logging).
  • retry repeats the thread execution several times when an error occurs, which is useful for transient errors such as network problems.

Without these operators, exceptions in RxJS can go unnoticed, especially when they occur in complex asynchronous chains.

Add catchError or retry to detect and handle exceptions:

import { throwError, of } from ‘rxjs’;

import { catchError } from ‘rxjs/operators’;

throwError(‘Error!’).pipe(

  catchError(err => {

    console.error(‘There was an error:’, err);

    return of(‘Default value’);

  })

).subscribe(value => console.log(value));

7. Analyzing performance and subscales

To optimize performance in Angular, it is important to monitor the number and state of RxJS subscriptions. Unclosed subscriptions can lead to memory leaks and affect the performance of the application. Too many subscriptions can also lead to excessive system load and unnecessary component reloads.

Recommendations for analyzing performance and managing subscriptions:

  • Use `async` pip in templates. It manages subscriptions automatically, prevents leaks and saves you from having to call `unsubscribe`.
  • Minimize the number of subscriptions. Instead of multiple subscriptions for the same data source, use combined operators like `combineLatest` or `withLatestFrom`.
  • Keep track of subscriptions in components. For threads bound to component lifecycles, use operators such as `takeUntil` or `first` for automatic termination.
  • Avoid superfluous threads. Check whether each thread is really necessary and remove unnecessary threads. Rethink the logic if several threads perform similar tasks.

Check performance with Angular DevTools. With this extension, you can determine how often data updates and component redraws related to subscriptions take place.

Proper management of subscriptions not only improves application performance, but also prevents potential errors and crashes when the application is running for an extended period of time.

In Angular, it is easy to overlook unclosed subscriptions. Use:

  • Async pip in templates to automatically manage subscriptions.
  • Angular zones to track changes and warn of infinite streams.

Conclusion

Debugging RxJS in Angular requires attention to detail and a deep understanding of the reactive approach. It’s important to actively use logging to track data and events in threads, and to use tools like DevTools to visualize observable performance.

By mastering these techniques, you will be able to quickly identify and fix problems and improve the stability and performance of your applications. This leads to a smoother user experience and reduces the likelihood of errors.