Debugging with the ng namespace

Alain Chautard

Angular 9 introduced the ng namespace variable, which is available in development mode but not exposed when the application is running in production mode.

We can debug an application using that global namespace without any breakpoint or dev tools extension. Here’s how.

First, select a DOM element

Using your browser dev tools, select a DOM element on the page as follows:

When an element is selected using the above process, it becomes assigned to a variable called $0 in the developer tools console. The previous selection is known as $1, the one before that $2, and on and on.

Then, use the ng workspace functions

If the selected DOM element is an Angular component, you can head to the browser console and type ng.getComponent($0). This returns a reference to the component instance – ready to be explored and debugged:

If the element you select is not a component (say a div or an image), use ng.getOwningComponent($0) to get a reference to the parent component of the selected DOM element.

If you want to select the directives applied to that element, use ng.getDirectives($0). It’s also possible to access the context of a template in a ngFor or ngIf directive.

There are a few more useful functions available in that global namespace.

Angular DevTools Extension

Alain Chautard

Angular DevTools is a browser extension that provides debugging and profiling capabilities for Angular applications (v12 minimum). It’s available for Chrome, Firefox, and Edge.

The extension comes with a tree view of the component hierarchy of our application. You can expand and collapse components to inspect their properties, inputs, and outputs. Hovering a component in the tree view highlights it in the user interface, as shown here:

We can explore inputs and outputs and even change those values to test how the UI would respond to different values:

There’s also a search feature where you can type the name of a component to find it in a complex component hierarchy:

Those features alone can be a huge time saver—no need for debugger breakpoints or JSON pipe to inspect our data. The inspector always displays up-to-date component information.

Angular 16 is coming soon!

Alain Chautard

It’s official; Angular 16 will be released on May 3rd. The first release candidate version is available, and yes, it includes the base API for Signals!

Signals will be in developer preview only for now, but we can expect the feature to be shipped and fully available with Angular 17, which is exciting news.

Other notable features include required inputs with @Input({required: true}) and the ability to receive router data as component inputs (think resolver data and URL params, for instance).

Of course, I’ll cover all these new features in more detail when the final version is released.

New Workshop Available

In the meantime, if you want to practice your RxJs skills, build custom directives, use content projection, and more, I just launched a workshop made of 7 different exercises with commented video solutions.

As a thank you for subscribing to this newsletter, the coupon code ng-newsletter gives you $20 off this $39 course (more than 50%), making it just $19 for the next 30 days.

A real bargain for Angular level 2 developers who want to prepare for the level 3 certification, for instance.

As always, let me know if you have any questions.

RxJs skipWhile operator

Alain Chautard

Our RxJS operator of the week is skipWhile. This operator will ignore values emitted by an Observable as long as a given condition is true.

Its marble diagram looks like this:

The above example shows us that as long as the emitted values are less than 5, they get skipped.

What are some everyday use cases for skipWhile? Here is an example where I want to wait for the user to type at least two characters in a form input before we start filtering (an addition to last week’s startWith example):

That way, the filter$ observable starts emitting values only when the source FormControl value has a length of at least two characters, which results in the following behavior:

This can be used to delay querying a server-side API with HTTP to start filtering only once we have enough meaningful data. This is somewhat similar to what can be done with the debounceTime operator.

You can see the complete example here on Stackblitz.

How to internationalize your Angular application?

Alain Chautard

Yesterday, we touched on how to change the locale of our Angular applications. The next step is to fully internationalize our apps by translating all text into different languages.

While Angular has its localization implementation to internationalize applications, the most popular library used for such a task is ngx-translate.

Why not use Angular’s internal implementation? The main reason is that Angular builds one version of your application per locale. As a result, if you have to support 20 different locales, your Angular build would output 20 different applications. This means that changing the site would result in a complete reload of the application. This also means that changing a translation requires a complete rebuild and redeploy of the application.

ngx-translate is much more flexible because it relies on pipes, directives, and services to translate our text at runtime instead of build-time. Here are some examples:

With TranslateService:

With TranslatePipe:

With TranslateDirective:

Translations come from specific files where translation keys ("HELLO" in my example) are mapped to actual values in each language. ngx-translate supports different formats out of the box (such as JSON and PO).

Here is an example of English translations stored in en.json:

And the same translations in French in fr.json:

All we have to do is indicate where the translation files are located and ngx-translate will download them as needed based on the locale.

Defining which languages are supported as well as which one to use by default can all be done with the TranslateService from the library:

You can see a live example of ngx-translate in Stackblitz here. If you want to try it, you can use my ngx-translate step-by-step tutorial.

How to change the locale of your Angular application?

Alain Chautard

A locale is a combination of country and language, such as fr-CA for French spoken in Canada or en-US for English spoken in the US. Locales matter when you want to create an application that works all around the globe.

For instance, let’s take the following sentence in American English for the US:

On 04/01/2023, the price of this item was $2,056.23

The same sentence in French for France would be:

Le 01/04/2023, le prix de cet article était 2 056,23 €

As you can see, everything is different. Currency, number format, date format, and of course, language. Knowing all of these differences between locales would be a complex task. Fortunately for us, Angular knows about most locales, and all pipes and formatting functions use that locale to format dates/numbers/currencies correctly.

To support different locales, we have to import all of them in main.ts:

Then you can configure your providers to set a default LOCALE_ID:

And just like that, the expression {{ 2056.23 | number }} would display 2 056,23 instead of 2,056.23 (code example here). So our pipes will use that default locale from now on.

Partial utility type in Typescript

Alain Chautard

Typescript is excellent for type safety as it prevents us from making mistakes when declaring new objects. That said, an object is sometimes created by aggregating data from different sources (different API calls, for instance).

For instance, say we have the following interfaces:

We have to create an instance of the Question object, but let’s imagine that creating that object requires several steps. In the first step, I retrieve data for the question itself, and in the second step, I have to retrieve the list of options.

At first, my Question object would look like this:

But this code won’t compile, as myQuestion is missing the options property. We could assign an empty array to options, or we could make it optional in the interface using this syntax: options?: Option[];

All of that seems like cheating, though. Instead, we can use the Partial utility type to indicate that our object is in a temporary state:

The compiler is happy with the above code; we don’t have to change our interfaces.

myQuestion is now an object that implements a subset of the Question interface, with all properties marked as optional.

Typescript has several more utility types like Partial. I’ll cover more of those in the upcoming newsletters.

RxJs startWith operator

Alain Chautard

startWith is an operator that does something straightforward: It takes an existing Observable and makes it emit a default value immediately.

Its marble diagram looks like this:

What are some everyday use cases for startWith? Here is an example where I want to display a loader while data is being loaded from a service:

The loading property is used to decide when to show/hide a loader. This observable would first emit { data: null, loading: true } then the actual data with loading: false.

You can see the complete example here on Stackblitz ( I had fun with Typescript, the async pipe, and generics in that example, too).

A more complex example in this tutorial is Dynamic filtering with RxJs and Angular forms. I describe how to create a text input used to filter a list of states as follows:

We need startWith in that scenario to start the filtering feature before the user has typed anything in the text input. That’s one of the most common use cases for the startWith operator.

Named router outlets

Alain Chautard

Using the Angular Router is one of the best ways to emulate multiple pages/screens in an Angular application. However, we might sometimes want even more flexibility by having the equivalent of “sub-pages” where sibling elements on a web page can display dynamic content based on the current URL.

Something like this where three different divs can display different components without a parent/child relationship:

Angular allows us to have named router outlets to support such scenarios. We can define several sibling outlets by giving them distinctive names like so:

Then, in our router config, we can define which component goes in which outlet for which path:

Finally, when routing a component to an outlet, we have to repeat some of that config in the form of a rather lengthy command:

The above code will load two different components in two different named outlets. You can see a live example on Stackblitz here.

Using a resolver function or a title strategy to change the page title

Alain Chautard

Before we get into today’s topic: The Angular Team’s Request for Comments (RFC) for Angular Signals is now open to the public. Feel free to take a look and give your feedback.

Yesterday, we saw how to change an application’s title using the router config. Today, let’s cover more complex scenarios when we need a dynamic title set depending on other factors.

Using a resolver function

First, we might need some processing using a function to extract information from a service or API. In that case, we can use a resolver function that gets that data and returns it:

Note that the signature of that function allows us to return a string, an Observable, or a Promise. That way, we can make an API request to fetch some extra data if needed. For instance, in the above example, getUsername() returns an Observable (code here). This is another excellent example of using the inject function we covered earlier in this newsletter.

Using a title strategy service

For more complex scenarios, Angular allows us to create a custom TitleStrategy. Such strategy takes the form of a service that has to implement an updateTitle method:

Here is an example where I add a prefix to the title, then use the default title from the title property in the router config. Note that we could easily inject other services and perform async operations before setting the new title if needed:

Such title strategy service has to be provided as the default title strategy in our dependency injection configuration as follows:

You can see that example in action here on Stackblitz.