APP_INITIALIZER Token in Angular (Advanced, 2022)

In real Angular applications, it might happen that you need to perform some logic or pull the data even before Angular will start rendering the very first component. So basically, we want to have something like ngOnInit lifecycle hook but for the whole application. This is where the APP_INITIALIZER token in Angular comes into play! In this video, you will see how to use this token and what you should pay attention to. If you find this video useful you can support my channel by sharing this video on your Social Media!
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🕒 Time Codes:
00:00:00 - Intro;
00:00:20 - Why would we need to hook into the app initialization process?
00:02:30 - Basic APP_INITIALIZER usage;
00:09:56 - Feature Description;
00:10:54 - Feature Implementation (fetching config from the server);
00:23:18 - Outro;
🔗 Source code on GitHub (init state on the master branch):
github.com/DMezhenskyi/angula...
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#angular #angular14 #angularadvanced #ng

[@DecodedFrontend]

If you want to support my channel and you find my content useful I would be grateful if you share it with your colleagues and friends. Thank you!🙏

[@p.s29]

Already did! 😁

[@DecodedFrontend]

Thanks a lot, Prateek! ;)

[@DecodedFrontend]

@Arsalan Majeed much appreciate it, Arsalan🙏🏻

[@claudiuciprianbetiuc3985]

Constantly doing it :) You have great content!

[@dimitridovgan6364]

Best Angular Tutorials!

[@oleksandrvorovchenko8674]

Great and useful as always! Thanks.

[@ayoubalfurjani4531]

This video was just right!, and my use case was exactly the same as the one mentioned in the example.
Overall a great video. Keep it up

[@OscarAndresPabonEstrella]

Your videos have helped me a lot, is not easy to find those kind of advanced things related with angular. Thanks a lot :)

[@innocentmazando3808]

I knew I was gonna need this video and now I am using it at work.
Thanks for the great video sir

[@mohamedsami5078]

Great content as always.

[@yorikworld]

Дякую, крутий контент.

[@Nabulio85]

Dmytro, award of best Angular instructor 🙏
Thank you very much.

[@user-rg7ij6yo8t]

Great tutorial and very informative, thanks!

[@nanasarathi]

You are a very good teacher... it was very informative. Thanks for sharing this video.

[@TheNicoad]

Your youtube channel is pure gold bar, hope you know it and feel good about it

[@MP3D2Y]

Nice video! Now I can understand better what is happening behind scenes when using that token privider

[@alextiger548]

Good stuff. Thank you!

[@djedaaa2232]

Helped me! Gread video!

[@malyna]

Чудове пояснення, думаю було б круто зробити окрему серію відео по розбіру сорсів!

[@thesweetvishu]

Great one...

[@andrija-official]

Great! Thank you

[@malbarmavi]

super good 😭😁👏👏

[@dimitritsikaridze6220]

Great content as always. video tutorial on angular elements would be nice there isn’t much on youtube that is up to date

[@vitaliyboyanivskyy1225]

Дякую за контент)

[@DecodedFrontend]

Будь ласка 😉 Заходьте ще))

[@user-fg6ng7ej6w]

очень толковые содержательные видосы, спасибо. вся эта серия про DI крута

[@horic007]

Awesome content! 👏🏻

[@DecodedFrontend]

Thanks! Glad you liked it:)

[@demidovmaxim1008]

Cool. Thank you for this video!

[@DecodedFrontend]

You are welcome :)

[@MarceloLopesS]

Hi, would you mind making a video about push-based architecture? I'd love to learn more how to use it and why. Reactive Angular seems very sophisticated

[@innocentmazando3808]

Powerful content as usual, thanks man

[@DecodedFrontend]

Glad you liked it! :)

[@sechabamothobi2616]

Amazing

[@volodimiryemshyn715]

Nice, thanks you. Lately I had problem with one task. I used resolver but I can't use it in app component, this way will help me. You are really nice person!!!)

[@vlads3856]

Awesome content!

[@DecodedFrontend]

Glad you enjoyed it!

[@ansumanmishra9608]

Great tutorial! Keep up the good work 🙂

[@DecodedFrontend]

Thanks, will do! :)

[@ianvink]

This was an excellent video.

[@DecodedFrontend]

Glad you enjoyed it!

[@shumilus]

Thanks

[@ivanco_s]

cool, thanks for making content like this 🙂

[@DecodedFrontend]

My pleasure!

[@Nurtylek]

I don’t think it’s a good idea to subscribe inside service, u could do it inside tap operator

[@vigneshwaran6410]

Awesome content😃, make more videos like this.

[@DecodedFrontend]

Thank you, I will

[@sandeepdravidam7989]

Great Content n Awesome way of explaining as always. Can u make a video on how to do
@supercharge/promise-pool npm package like flow in Observable way . It would be great video to learn. It would be challenging for u n great learning for us 😉

[@vpeti88]

Thanks for the excellent videos!
Can you help me? Can you make a video about a plugin architecture with auto discorvery, anyway it's possible in frontend framework?

[@JoeBoo532]

Hi, could you please explain the benefits of assigning the response results to an observable instead of just using an array? Thank you!
loving your vid by the way! :D

[@exsitewebsolution6803]

hi great tut as usual! Could app_intializer be used to create a webmanifest dynamically? so that we can white label our APP to suit multiple customers.

[@jakubdrewniak2668]

that is really nice approach, I didn't know that. but how does it different from making this kind of initialization in AppModule constructor? are there any advantages besides blocking app initialization before data from api is resolved? (of course this is huge advantage, I'm just wondering if there are more?)

[@DenisBendrikov]

Thanks a lot for showing how it works under the hood.
Also it is worth mentioning that APP_INITIALIZER doesn't work if used in lazy loaded feature modules

[@DecodedFrontend]

Thank you for the addition! You are absolutely right.
Regarding 'under the hood' stuff, should I do dive more in the source code? :)

[@DenisBendrikov]

@@DecodedFrontend in your videos you do a great job with a high-level source code overview 👍 so I better leave you the choice of how deep you should dive

[@DecodedFrontend]

@@DenisBendrikov got you! Thanks 😊

[@blokche_dev]

👍 Thanks for the valuable content you create and share. Do you plan to dig further into Angular CDK?

[@DecodedFrontend]

Thanks for the feedback! Yes, I plan also the course about CDK :)

[@isasunasra9910]

Hello, first of all, thank you for all the amazing content.
I wanted to know if there's a way to show some loader while APP_INITIALIZER is doing its job.

[@johnlambertasis6620]

Thank you sir, but can u do a tutorial about MEAN stack like doing something projects such as cloning twitter, facebook or something that can be cloned. Highly appreciated all your videos sir! Keep it up!

[@deniskoliban6664]

Great video, thank you Dmytro😃. I think you don't need to use asObservable() if you use pipe() on BS, because pipe returns an observable)

[@DecodedFrontend]

Hi Denis! it is a good point that made me actually investigate this a little bit this question and I found something interesting :) It turns out, that .asObservable() and .pipe() are not completely equivalent. The pipe() on BS returns actually the BehaviorSubject but the trick is that the .pipe() method narrows the return type to Observable, so TypeScript won't allow you to call the next() method though it actually BS. You can hack it using something like that `(this.endpoints.pipe() as any).next('value')` and in such a way emit a new value to the stream. But when you do `(this.endpoints.asObservable() as any).next('value')` you will get an runtime error because asObservable() returns actually the Observable that doesn't have next() method at all :) So... it seems like asObservable() is safer/stricter but while you use TypeScript I think it is ok to use both approaches.

[@hoangducnguyen8887]

Hey @DecodedFrontend, what's your desk setup?

[@Afdac247]

Also in addition I have a problem with my bundle sizes if you ever worked with three.js you will know that they don't have esm modules, so no tree-shaking and there for the whole 500 kb gets bundled into the final app, I feel that I would have to download the package in a standalone project rebuild it some so their exports can be converted to be available as es import would you like to connect to discuss

[@alpinestylecom]

Great Video. Why not just use a classic resolver for App Component instead?

[@DecodedFrontend]

Thanks for the question! A couple of reasons:
1) Resolvers will be invoked after the App Component is created.
2) Resolvers are used when you resolve some data for some certain route but app config usually isn't something that depends on the Router.

[@miroslavpetrov3006]

Great, now how do I preload my LCP image

[@_Greenflag_]

Why do you need to convert a behaviourSubject, which is an observable, to an observable using asObservable( ) method ? To use a copy of it, similar to the slice ( ) method on array ?

[@1997jugulator]

I'm wondering what is the benefit from using asObservable in service?

[@m3kbeatz]

But why app_initilazier doesn't block imported modules?

[@AlphaFrog1021]

there aren’t many tutorials on angular SSR

[@sunilvilluri385]

@Decoded Frontend - I want to know how you are able to see the actual code implementation instead of d.ts files. Can you provide steps to do it

[@chikkachokka3401]

you got it sunil? if yes, can you please share?

[@sunilvilluri385]

@@chikkachokka3401 - there is a shift between editors which was trimmed in editing. There is no straight way to get it

[@beratsulimani9823]

Hi Dimitry,
Thanks for the great content, can APP_INITIALIZER be used for a fully standalone project.

[@DecodedFrontend]

Do you mean if the project uses standalone components?

[@beratsulimani9823]

@@DecodedFrontend Yes Dimitry, without ngModules how APP_INITIALIZER can be used?

[@DecodedFrontend]

@@beratsulimani9823 then you have to provide APP_INITIALIZER token in the ``` bootstrapApplication(AppComponent, {
providers: [
{ provide: APP_INITIALIZER... }
]
}) ```
like that

[@DecodedFrontend]

it is inside main.ts file

[@beratsulimani9823]

Thanks a lot Dimitry.

[@MrBan001]

What do i have to do if i want to use that config in another APP_Initializer?

[@DecodedFrontend]

You could save the fetched config in a separate service which is provided for the same injector where APP_Initializer token.

[@Alessandro_Russo]

When a complete overview about providers?

[@DecodedFrontend]

What do you mean?

[@Alessandro_Russo]

An explanation of how providers work. I found it already you did thanks.

[@olegshyshka5948]

Thanks for support the Ukraine.

[@haroldpepete]

brutal video, if you ever need a liver or heart, let me know

[@denysdzhelomanov2633]

You don't need to write asObservable function before pipe, pipe func does the same job

[@DecodedFrontend]

Hi Denys! Thanks for your comment :) I already answered a similar comment, so if you don't mind I will just duplicate the answer here: "it is a good point that made me actually investigate this a little bit this question and I found something interesting :) It turns out, that .asObservable() and .pipe() are not completely equivalent. The pipe() on BS returns actually the BehaviorSubject but the trick is that the .pipe() method narrows the return type to Observable, so TypeScript won't allow you to call the next() method though it actually BS. You can hack it using something like that `(this.endpoints.pipe() as any).next('value')` and in such a way emit a new value to the stream. But when you do `(this.endpoints.asObservable() as any).next('value')` you will get an runtime error because asObservable() returns actually the Observable that doesn't have next() method at all. So... it seems like asObservable() is safer/stricter but while you use TypeScript I think it is ok to use both approaches"

[@hubert.t4243]

Hi Dymitro. To go further up the tree, can I also use PLATFORM_INITIALIZER within the argument of platformBrowserDynamic in the main.ts and this will resolve before anything resolved within the APP_INITIALIZER. Thanks

[@DecodedFrontend]

Yes, it is. PLATFORM_INITIALIZERs are being executed befor APP_INITIALIZERs :)