Angular

Debugging Strategies for Angular Applications

Published Feb 14, 2022

Updated May 30, 2023

7 min read

This article was written over 18 months ago and may contain information that is out of date. Some content may be relevant but please refer to the relevant official documentation or available resources for the latest information.

When programming, a lot of time is spent reading and debugging code. When coming to grips with a new framework or library, it is important to know how to debug it when things eventually go astray. Angular has a plethora of useful 1st party and 3rd party tools that will aid you in debugging your application effectively.

Angular Devtools

First thing’s first, if you don’t have the Angular Devtools already, then you should download them. The Angular Devtools does many things such as allowing you to view the component tree live as your application runs, view the state of components in your application, and profile your application.

Below, I have an Angular application loaded, and I can view the internal state and configuration of the various components present.

There is also a “Profiler” tab that can be used for measuring the performance of your individual components. You may ask what performance profiling has to do with debugging. Performance issues are problematic like any bug, and can lead to a detrimental user experience. Being able to identify these issues will make it easier for you to fix these issues, and improve the application.

The profiler gives us a breakdown of the resources used by each component. This is very useful for identifying performance bottlenecks in your application.

One last thing I should mention is the ability to jump to the source code of the component you currently have selected. The button looks like a pair of angle brackets in the top-right corner. This is useful if you need to use the built-in debugger provided by the browser. I highly recommend reading up on the official guide for Angular Devtools, which goes more in-depth about the various features.

Using a JavaScript Debugger

Do not forget that your browser has a built-in debugger. Angular application dev builds are very debuggable as source maps are provided by webpack. If you’re using the Angular CLI for your developer server, then you should already be good to go!

You can access your source code through the “Sources” tab, and it will be available under the “webpack://” dropdown. However, it isn’t very convenient to navigate your source code like this. Instead, you can search for your TypeScript files using CTRL+P (or CMD+P on mac), or use the Angular Devtools to jump to the source code of your components.

Once you’re in the source file, you can place breakpoints directly in your TypeScript files! Do note that debugging the original TypeScript files is not available in production builds.

You should try to use the debugger over “console.log” in most situations. It will be much easier to view the state of your application here, and understand what is going on.

Redux Devtools

Lots of Angular applications are using NgRx for state management now. One important thing to keep in mind is that NgRx is compatible with the Redux devtools browser extension. Although NgRx is not based on Redux, that does not stop it from being compatible with its developer tools! Isn’t that neat?

You can install the Redux devtools from your browser’s respective extension marketplace. Once it’s installed, you should see a new tab when you open devtools (F12). Here, you can see I have loaded up a demo application that uses Redux, and the tools appear to be working!

Before we dig in deeper, I should mention that the application has to do some extra setup to ensure that Redux Devtools works. Out of the box, your application will not work with Redux Devtools until you import the StoreDevTools module. That can easily be done by adding another import to your module.ts file.

@NgModule({
  // Properties...
  imports: [
    // Other imports...
    EffectsModule.forRoot([TodosEffects]),
    !environment.production
      ? StoreDevtoolsModule.instrument({
          name: 'TodoMVC app using Angular & NgRx',
          maxAge: 50,
        })
      : [],
  ],
  // Properties...
})
export class AppModule {}

There are a few things to describe on this screen. Let’s talk about the left sidebar. It is here that you will find a list of actions that have been emitted throughout the lifetime of the application. The first 5 actions are emitted by NgRx after performing initialization of the store and the router. Everything after those are from the application code for the particular example we’re using.

Clicking on one of the actions and having the “Diff” view action on the right-hand side will show what state was changed by it. In the TODO MVC example I used, there are two actions that happen upon initialization. The first just updates a loading flag to true. Then, the second one adds the TODO entries and flips the loading flag back to false.

You can also view the contents of individual actions through “Action”, the overall state at that point in time with “State”, generate Jest tests that replay the creation of the state with “Test”, and use “Trace” to find the callstack of whatever triggered the action in the first place. The trace tab in-particular, can be very helpful if an action is being emitted unexpectedly, and you want to figure out why.

I did all of this analysis against the todomvc-angular-ngrx repository if you want to try using the Redux devtools for yourself. We have only glossed the surface of the Redux Devtools here, and I could write a whole article about this wonderful piece of software, but we already did that! If you want to learn more, please consider reading our more in-depth article, Developer Tools & Debugging in NgRx.

Using ng.profiler for Identifying Change Detection Issues

We’ve already gone over the Angular Devtools profiler, but there is another tool provided by Angular that we can use for identifying performance issues related to change detection. For the uninitiated, change detection is the mechanism by which Angular checks for changes to your application’s state, and re-renders views when it does happen. Sometimes, change detection may cause performance issues in larger applications, and one easy way to find out if this is harming it is to use ng.profiler.

ng.profiler can be run on the browser’s console once it is enabled. To enable it, you must call “enableDebugTools” after your app module is finished initializing. I recommend only doing this for dev builds.

platformBrowserDynamic()
  .bootstrapModule(AppModule)
  .then(moduleRef => {
    if (!environment.production) {
          const applicationRef = moduleRef.injector.get(ApplicationRef);
          const componentRef = applicationRef.components[0];
          // Ensure that `ng.profiler` exists.
          enableDebugTools(componentRef);
    }
  })
  .catch(err => console.error(err));

With this code in “main.ts”, we can now use ng.profiler.

Hurray, it works! As you can see, there’s no problem with change detection in our current view of the application. If there is a problem however, there is an extra option that you can specify to get more fine-grained details. Pass the “record” option into ng.profiler like so.

To view the results of the profiling we must ensure that the JavaScript Profiler is enabled (note: this is Chrome specific). You can enable this feature via the Devtools Hamburger Menu > More Tools > JavaScript Profiler.

Once that’s enabled, you should have a new “JavaScript Profiler” tab that contains your results!

This may look a little intimidating because you will see a lot of results for functions that you don’t have direct control over. Essentially, this is a breakdown of the amount of time it takes for functions in your project to execute. You can sort by total time spent to identify bottlenecks being caused by JavaScript execution as a result of change detection being triggered.

Since the code in my example is fairly minimal, you’re only going to see function calls from the libraries we are using. In a heavier real-world application, you will likely see references to functions in your own application if they’re doing a lot of work on the CPU.

Conclusion

When encountering difficult bugs, whether they’re performance related or otherwise, it helps to know what tools are at your disposal. I hope this information proves useful in your future bug hunts!

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

We love helping teams with projects that have missed their deadlines or helping keep your strategic digital initiatives on course. Check out our case studies and our clients that trust us with their engineering.

About the author(s)

Jamie Kuppens
I’m a software engineer with an interest in web development and some more esoteric things like emulator development.
@Reshurum @Reshurum

Angular Signals for Simpler State Management and DOM Performance

In this episode of the Modern Web Podcast, host Rob Ocel is joined by Adam Rackis, Danny Thompson, and guest Braydon Coyer, Senior Front-End Developer at LogicGate to talk about using Angular Signals for improved state management and DOM performance. Braydon explains how Signals simplify Angular development and offer better readability and efficiency compared to traditional methods like RxJS. The conversation also touches on hiring in the AI era, discussing challenges around take-home tests and live coding, and how AI tools like ChatGPT are changing the interview process. Chapters - 00:00 - Introduction - 00:57 - The Angular Renaissance - 02:24 - Signals in Angular - 03:27 - Transitioning to Signals - 04:19 - Signals in Utility Development - 05:09 - RxJS and Signals - 07:52 - Signals vs Other State Management Solutions - 09:34 - Testing Signals - 10:29 - Control Flow and Standalone Components in Angular - 12:02 - Angular's Evolution and Accessibility - 13:28 - Angular’s Framework Governance - 17:10 - Hiring in the Age of AI - 19:15 - Pair Programming and Real-Time Problem Solving - 22:24 - The Role of AI in Interviews - 27:58 - Wrapping Up Follow Braydon Coyer Twitter: https://x.com/BraydonCoyer Linkedin: https://www.linkedin.com/in/braydon-coyer/ Github: https://github.com/braydoncoyer...

Oct 30, 2024

1 min

Angular

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

The HTML Dialog Element: Enhancing Accessibility and Ease of Use Dialogs are a common component added to applications, whether on the web or in native applications. Traditionally there has not been a standard way of implementing these on the web, resulting in many ad-hoc implementations that don’t act consistently across different web applications. Often, commonly expected features are missing from dialogs due to the complexity of implementing them. However, web browsers now offer a standard dialog element. Why use the dialog element? The native dialog element streamlines the implementation of dialogs, modals, and other kinds of non-modal dialogs. It does this by implementing many of the features needed by dialogs for you that are already baked into the browser. This is helpful as it reduces the burden on the developer when making their applications accessible by ensuring that user expectations concerning interaction are met, and it can also potentially simplify the implementation of dialogs in general. Basic usage Adding a dialog using the new tag can be achieved with just a few lines of code. ` However, adding the dialog alone won’t do anything to the page. It will show up only once you call the .showModal() method against it. ` Then if you want to close it you can call the .close() method on the dialog, or press the escape key to close it, just like most other modals work. Also, note how a backdrop appears that darkens the rest of the page and prevents you from interacting with it. Neat! Accessibility and focus management Correctly handling focus is important when making your web applications accessible to all users. Typically you have to move the current focus to the active dialog when showing them, but with the dialog element that’s done for you. By default, the focus will be set on the first focusable element in the dialog. You can optionally change which element receives focus first by setting the autofocus attribute on the element you want the focus to start on, as seen in the previous example where that attribute was added to the close element. Using the .showModal() method to open the dialog also implicitly adds the dialog ARIA role to the dialog element. This helps screen readers understand that a modal has appeared and the screen so it can act accordingly. Adding forms to dialogs Forms can also be added to dialogs, and there’s even a special method value for them. If you add a element with the method set to dialog then the form will have some different behaviors that differ from the standard get and post form methods. First off, no external HTTP request will be made with this new method. What will happen instead is that when the form gets submitted, the returnValue property on the form element will be set to the value of the submit button in the form. So given this example form: ` The form element with the example-form id will have its returnValue set to Submit. In addition to that, the dialog will close immediately after the submit event is done being handled, though not before automatic form validation is done. If this fails then the invalid event will be emitted. You may have already noticed one caveat to all of this. You might not want the form to close automatically when the submit handler is done running. If you perform an asynchronous request with an API or server you may want to wait for a response and show any errors that occur before dismissing the dialog. In this case, you can call event.preventDefault() in the submit event listener like so: ` Once your desired response comes back from the server, you can close it manually by using the .close() method on the dialog. Enhancing the backdrop The backdrop behind the dialog is a mostly translucent gray background by default. However, that backdrop is fully customizable using the ::backdrop pseudo-element. With it, you can set a background-color to any value you want, including gradients, images, etc. You may also want to make clicking the backdrop dismiss the modal, as this is a commonly implemented feature of them. By default, the <dialog> element doesn’t do this for us. There are a couple of changes that we can make to the dialog to get this working. First, an event listener is needed so that we know when the user clicks away from the dialog. ` Alone this event listener looks strange. It appears to dismiss the dialog whenever the dialog is clicked, not the backdrop. That’s the opposite of what we want to do. Unfortunately, you cannot listen for a click event on the backdrop as it is considered to be part of the dialog itself. Adding this event listener by itself will effectively make clicking anywhere on the page dismiss the dialog. To correct for this we need to wrap the contents of the dialog content with another element that will effectively mask the dialog and receive the click instead. A simple element can do! ` Even this isn’t perfect though as the contents of the div may have elements with margins in them that will push the div down, resulting in clicks close to the edges of the dialog to dismiss it. This can be resolved by adding a couple of styles the the wrapping div that will make the margin stay contained within the wrapper element. The dialog element itself also has some default padding that will exacerbate this issue. ` The wrapping div can be made into an inline-block element to contain the margin, and by moving the padding from the parent dialog to the wrapper, clicks made in the padded portions of the dialog will now interact with the wrapper element instead ensuring it won’t be dismissed. Conclusion Using the dialog element offers significant advantages for creating dialogs and modals by simplifying implementation with reasonable default behavior, enhancing accessibility for users that need assistive technologies such as screen readers by using automatic ARIA role assignment, tailored support for form elements, and flexible styling options....

Oct 25, 2024

4 mins

HTMLJavaScript

Making Seamless Page Transitions with the View Transitions API

Make Seamless Page Transitions using the View Transitions API Traditionally web applications have always had a less polished experience, both functionally and visually speaking, compared to native applications on mobile and other platforms. This has been improving over the years with the introduction of new web APIs and standards. One such new API that bridges that gap is the View Transitions API. What is the View Transitions API? The View Transitions API is a new browser feature that allows developers to more easily create animated transitions between pages and views, similar to how mobile apps have transitions when navigating between pages. Adding view transitions to your application can reduce the cognitive load on your users and make the experience feel less inconsistent. One great thing about view transitions is that they can be used by both SPAs (single-page applications) and MPAs (multi-page applications) alike! Using the View Transitions API for SPAs Let’s see how we can use view transitions ourselves. We will use examples adapted from demos created by the wonderful Jake Archibald and Bramus. There are some alterations to a few of the examples to make them work with the newest version of the View Transitions API, but otherwise, they’re mostly the same. The process of getting view transitions working for SPAs is as simple as calling document.startViewTransition right before starting navigation and replacing your page’s content immediately after that. You need to make this call in your router or in an event listener that triggers your page navigation. The following is an example of how you can hook into page navigation in a vanilla JavaScript application. This example uses the Navigation API if it’s available. As of the time of writing this article only Chromium-based browsers support the Navigation API, but there is a fallback to using a click listener on link elements so that this works with Firefox and Safari. ` If you’re using a framework, then there’s probably a better way to do this specific to that framework than by using this contrived example. For example, if you are implementing usage of this API with a Next application, you may opt for something like next-view-transitions. For this article, we’re going to focus on the way this is done in vanilla JavaScript so that the fundamentals of using the API are understood. Knowing how it’s implemented in vanilla JavaScript should give you enough understanding to implement this in the framework of your choice if there isn’t already a library that does it for you. Now we have a way to know when a navigation is being requested. Using the above utility function we can start the animation and replace our content as follows: ` getMyPageContentSomehow can be any function that returns HTML. How that is implemented will depend on your application and framework of choice. If you want to run these examples on your machine, the demo repository has instructions in its README. In essence, it’s as simple as hosting an HTTP server at the root of the project and visiting localhost. No fancy build system is required! By default, a fade is done that only lasts for a moment. The animation that happens can be configured using CSS with the ::view-transition-group pseudo-element on the element you want to animate, which in our case is the entire page, and we pass in root. ` Given that the animation properties are used, you have much control over what kind of animation to do. You can change the duration and the interpolation, add keyframes and gradients, and even add image masks. You can learn more about the animation properties in CSS on MDN. Using the View Transitions API for MPAs As mentioned, view transitions also work for MPAs with no client-side routing. Setting up view transitions for MPAs is much easier than for SPAs. All you have to do is include the CSS rule on all pages where you want the animations. ` Of course, like how it works with SPAs, you can customize the animations to your heart’s content using the view transition pseudo-elements. Conclusion I hope this article helped you understand the fundamentals of using the View Transitions API. Now that most browsers support it and it’s not too difficult to add it to existing applications, it is a great time to learn how to use it. You can view a full list of examples here (made by Jake Archibald and Bramus) if you want to see how advanced the animations can get. I like the Star Wars ones especially. The README explains how to get all the examples up and running (a total of 43!)....

Aug 2, 2024

4 mins

JavaScript

How Nuxt Studio is Redefining Developer & User Experience with Baptiste Leproux & Ferdinand Coumau

In this episode of the Modern Web Podcast, Danny Thompson sits down with Ferdinand Como and Baptiste Leproux from Nuxt Labs to uncover the story behind Nuxt Studio, a tool that's transforming how developers and non-technical users interact with Nuxt applications. Ferdinand and Baptiste share how Nuxt Studio bridges the gap between developer customization and user-friendly content management. Built to empower agencies, freelancers, and their clients, Nuxt Studio combines powerful features like live previews, Vue component integration, and schema-driven forms to make managing content seamless. The conversation also explores the broader mission of Nuxt Labs—building sustainable open-source tools that enhance developer experience and meet real-world needs. With insights into the future of Nuxt Studio and its potential to scale for larger organizations, this episode is a must-listen for anyone passionate about innovation in web development. Chapters 1. Introduction and Setting the Stage (00:00:00) 2. The Vision Behind Nuxt Studio (00:03:10) 3. Nuxt Studio’s Core Features (00:08:45) 4. Challenges in Building Nuxt Studio (00:16:20) 5. Target Audience and Use Cases (00:22:35) 6. Sustainability in Open Source (00:29:00) 7. The Future of Nuxt Studio (00:35:10) 8. Nuxt Studio’s Role in the Nuxt Ecosystem (00:42:30) 9. Closing Thoughts and What’s Next (00:48:00) 10. Sponsor Shoutout and Wrap-Up (00:53:20) Follow Baptiste Leproux and Ferdinand Coumau Baptiste Twitter: https://x.com/_larbish Ferdinand Twitter: https://x.com/CoumauFerdinand Baptiste Linkedin: https://www.linkedin.com/in/baptiste-leproux-618842b0/ Ferdinand Linkedin: https://www.linkedin.com/in/ferdinand-coumau-nuxt/ Sponsored by This Dot: thisdot.co...

Nov 20, 2024

2 mins

VueNuxtJS

Let's innovate together!

We're ready to be your trusted technical partners in your digital innovation journey.

Whether it's modernization or custom software solutions, our team of experts can guide you through best practices and how to build scalable, performant software that lasts.

Debugging Strategies for Angular Applications

Angular Devtools

Using a JavaScript Debugger

Redux Devtools

Using ng.profiler for Identifying Change Detection Issues

Conclusion

Jamie Kuppens

You might also like

Angular Signals for Simpler State Management and DOM Performance

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

Making Seamless Page Transitions with the View Transitions API

How Nuxt Studio is Redefining Developer & User Experience with Baptiste Leproux & Ferdinand Coumau

Let's innovate together!

You might also like

Angular Signals for Simpler State Management and DOM Performance

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

Making Seamless Page Transitions with the View Transitions API

How Nuxt Studio is Redefining Developer & User Experience with Baptiste Leproux & Ferdinand Coumau