Angular APP_INITIALIZER is not delaying the app initialization when returning a promise, Angular 5 wait for promises to return from for loop, Angular 8 APP_INITIALIZER service start before loading config file, Angular imported modules do not wait for APP_INITIALIZER, Cannot handle OpenDirect push notification when iOS app is not launched. The sole purpose of this is to tell the run time what version of the code you want to run. They are all able to run simultaneously but the code will be stopped here until we get all the promises resolved. DEPLOY AN ANGULAR UNIVERSAL PROJECT TO AWS ELASTIC BEANSTALK, Infinite whiteboard with konvaJS and Angularpart 1. const asyncInitPromises: Promise[] = []; Promise.all(asyncInitPromises).then(() => { complete(); }).catch(e => { this.reject(e); }); configFoo = configurationFactory(http, configService, []); configFoo = configurationFactory(http, configService, [factory(dep1, dep2), functionDefinition]); One thing is certain that we need a static json file to store our configs so lets first create a config file and name it config.json. It will specify a factory and that will return a promise, the promise will load the config for the application. Take a look to the next code. I had to load some initial configuration data from three different endpoints before App Component is loaded. Build RESTful API Server with Deno and Docker, Javascript Intro to Pass by Value vs Pass by Reference, // Thanks for contributing an answer to Stack Overflow! Such factory will be used in the App Initializer provider. As you can guess, factory B and C will have a subscription to ready$ so they are notified when request A is done. BUT, the url of the server is in the application config (I cannot change that).

If the function that you provided will throw an error, the application will not be loaded. multi: true will allow to have multiple instances of the provider. Angular 2 - APP_INITIALIZER : wait for chaining promises, How APIs can take the pain out of legacy system headaches (Ep. What is the difference between Promises and Observables? As we are using HttpClient, well need to import HttpClientModule in app.module.ts, Now well add APP_INITIALIZER provider in app.module.ts as following. That means were using factory provider. Well this article will tell you where to store configurations and how to read them in Angular. To learn more, see our tips on writing great answers. We do that by using the deps: flag and let angular know that it needs to create a instance of AppInitService and inject it to the initializeApp1 function. Was there a Russian safe haven city for politicians and scientists? First we will need a service to save the configs we are getting from config.json so lets create a ConfigService. Here, weve created a method called loadConfigurationSettings() which will call api to get the configuration settings that we needed when the application starts. What most developers dont get about Object-Oriented Programming. It indicates that were providing APP_INITIALIZER. Well use this service to fetch the configuration that we needed before application starts. Now well see how to use APP_INITIALIZER in Angular Application, Run the following command to create a new application. As you can see in the above image, It has first fetched the github user and then App component is initialised., I hope you like this Angular APP_INITIALIZER token article. You can replace resolve(true) with your code or can write a new promise. There is a defined place for storing config in Angular and you should make most use of it. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Or a real array of functions for an integration test. (assuming youve already installed angular cli and if not then first install angular cli and then run the following command), Now create configuration service by the following command. With this second approach, there will be three factories, one for each request.

The first request is going to be to endpoint A. Ill make the HTTP request and will convert the Observable returned by get method to a Promise. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. need to create separate function which invoke the appInitService.Init() are returns a Promise. Easily deploy your Angular web app using Azure App Services. This service use HttpClient which will call out api endpoint and will get a settings from that api endpoint. Now you might be wondering whats APP_INITIALIZER injection token and where it is used. before loading the application ? We have already added this in deps of APP_INITIALIZER. So using map function I create a new Array of Promises and pass it to Promise.all() method. How to check Angular CLI version and how to update it. Did Sauron suspect that the Ring would be destroyed? If any of these functions return a Promise, initialization does not complete until the Promise is resolved.

APP_INITIALIZER is run when the application starts to initialized. The multi : true create the multi provider, Make sure you enter the(*)required information where indicate.HTML code is not allowed. Observables added unnecessary complexity to ConfigurationService which will make our implementation harder to understand and test. How can I wait for all my promises to be achieved in the right order How can I make sure that my config AND my user is set before everything else ? After loading the configs you can resolve the promise. This is good because each factory will have injected its own dependencies only. It will call the initialize method. With this definition we can reuse the existing factories as they already createaFunctionthatreturnsaPromise. It means we could have multiple APP_INITIALIZER providers, not just this single provider. When adding a new disk to Raid1 why does it sync unused space? It means were injecting ConfigurationService as dependency. Lets find a way to remove coupling. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide.

Now in your unit test for configurationService you dont have to create a spy or any other trick for the dependent functions, just pass an empty array for the configDeps. But is this recommended? I tried this in my application module but the application starts right after the config is loaded, and doesn't wait for my user service. Is possible to extract the runtime version from WASM file? Each one needs to be provided using a factory that will return the function executed by Angular. However, in order to load configuration from endpoint B and C, I had to get first the base URL from endpoint A. Angular has a hook in its process of initialization called App Initializer. Follow-up: Number of points on an elliptic curve, How to encourage melee combat when ranged is a stronger option. APP_INITIALIZER is an injection token that allows you to provide one or more initialization functions. Help us improve this content by Endpoint A contains some core configuration such as base URL. ConfigurationService will have a ready$ Observable property that will emit a stream when configuration data has been set after request A is resolved. And thats how we deal with config in Angular. Lets keep factories decoupled but lets get rid of complexity of Observables in this early phase of the application, keeping ConfigurationService untouchedandthingssimple. we cann't do it directly from the provider. I will not delete the post because it might help other people who wants to know how to wait for several promises to be done before loading the application. In this article, were going to learn how to use Angular APP_INITIALIZER injection token. Making statements based on opinion; back them up with references or personal experience. Connect and share knowledge within a single location that is structured and easy to search. This token allows you to provide multiple App Initializers. rev2022.7.21.42635. Cool! if any of the initializers returns a promise then the angular waits for it to resolve, before continuing with the app initialization. Can a timeseries with a clear trend be considered stationary? Is "Occupation Japan" idiomatic? Example: and add them as parameter to our initialize method. So it's solved. loading environment config and then calling a userService. When you want to load the application configuration when the application starts, youll need to use APP_INITIALZER. This ensures that the configuration will always be read when your application is loaded. It uses the simplicity of nesting dependent requests of solution one and creating multiple factories from solution two, but in this case Im going to provide only one App Initializer and a custom Injection Token that will handle factories B and C. ConfigDeps is the new Injection Token of type (() => Promise)[]. 465). For example, you might want some settings like apiUrl, apiKey, imageBaseUrl, languages etc. As you can see in the above code, weve added provider in providers array. I was trying to do exactly the same thing ! userFactory: configurationProviderFactory. Cause it was never meant to store configurations in this file. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. These functions are injected at application startup and executed during app initialization. Love podcasts or audiobooks? The useFactory is used because initializeApp1 is a function AppInitService to be injected as the argument. Different ways to install bootstrap 4 in angular application, How to define global constants(variables) in angular, How to install angular material in Angular Application, How to change angular port from 4200 to something else. What should I do when someone publishes a paper based on results I already posted on the internet? from Twitter An App Initializer is a special kind of Injection Token identifier of a dependency of type Array of Functions that is executed when an application is initialized. I'm using the APP_INITIALIZER to load application config before everything else. Register the dependency in the provider using token, the token eithe type, a string or a instace of InjectionToken, Angular Dependency injection injects to dependencies to classes & components, not a function. As told above, this will return a promise. editing this page on GitHub, Writing and Reading JSON config file in Python, Writing and Reading XML config file in Python, Writing and Reading YAML config file in Python, Top 4 Must Have Skills For A Project Manager, Access internet on Linux using Android Tethering, Writing and Reading config files in Angular, Abstract classes and interfaces in Python, Deep Learning helped reducing variability in Cardiovascular Imaging, Difference between append and extend in Python, How to print on same line with print in Python, Writing and Reading config files in Python. Now lets use initialize method to read our config file and set the necessary details for our app. we need to execute the appInitService.Init(). Now if youll run the application using ne serve, you can see that below output. No, right? Notice that ConfigDeps is now a dependency for configurationFactory. Once I get the response from endpoint A, Ill set configuration data into ConfigurationService instance and then Ill make requests B and C. The problem that I identified in this solution is that adding or removing a dependent function will force me to touch not only its own function, but also configurationFactory where dependent functions live. A few days ago I faced a problem with Dependency Injection in Angular. Now, I also have to get the current user by asking the server. I came out with three possible solutions for this problem, lets examine them one by one: In this case, I will handle all requests in one single place, configurationFactory. Wait until all promises complete even if some rejected. What is if __name__ == "__main__" in Python. How do I convert an existing callback API to promises? Every app has some configurations to load. Find centralized, trusted content and collaborate around the technologies you use most. It will look something like this: Now we have config.json but we will need a place for it. Itll allow you to provide a function which will be executed during the application bootstrap process. Lets say we need to store the baseUrl of our app. This function can return a Promise. Although this is a very specific scenario using App Initializers, the thought process should be the same when solving similar problems that have to do with dependency in Angular. Finally, Im going to inject this new Injection Token into configurationFactory making this factory oblivious of the configuration dependency functions. Thus the above array of functions will be injected to configurationFactory. I had forgot to add the "return" statement in the setCurrentUser promise. Announcing the Stacks Editor Beta release! If you wonder, I had considered at the beginning to just provide three App Initializers in a specific order in which they need to be executed, then I realized that they all are executed at the same time using Promise.all(). so it useful when you want to load some data before application starts. So lets move to our actual solution which is: Sounds awesome right? The most common is environment configurations which are required when you have multiple environments - local, dev, qa, uat and prod. This is working fine. To add dependencies, add a deps section in its provider. No! Thank you. I know this comes as first option in our mind but can you see config in its name? One option is to have it in assets or dist and use it to get and set the configurations. , Angular Single Image Upload With Preview Example, How to use environment variable in Angular application, Integrate CKEditor(rich text editor) in Angular. It just knows that theres an Array of Functions that need to be executed once request A is resolved. How To Add Google Analytics to Your Vue.js Web App. If the Promise is resolved then it will continue with the initialization, otherwise, if the Promise is rejected then an error will be thrown and will exit the application. Asking for help, clarification, or responding to other answers. Scientifically plausible way to sink a landmass. Where do you think this should be added? As said above, App Initializers will be executed at the same time by Angular, so there must be a way for request B and C to wait until A is ready, since they are not nested anymore. Well call this method from factory. Now you may argue that we can create different environment.ts files for different versions, yes you can but again this is not the purpose of this file. In this code sample we have added APP_INITIALIZER to app.module.ts. This solution is a combination of solutions one and two. useFactory will have the function which will return a function which will return a promise.

To subscribe to this RSS feed, copy and paste this URL into your RSS reader. What's inside the SPIKE Essential small angular motor? You can use this method to load configurations and initialize your app. We ended up with a solution that is maintainable and easy to test at the same time. Our app.component.ts will log App Component initialized as following: Thats It, weve successfully implemented APP_INITIALIZER token. All we have to do next is to use the factories for creating the functions, put them into an array and return the array. When it comes to dependency issues, why dont we use Angulars Dependency Injection system?, isnt that what it was made for? Could a license that allows later versions impose obligations or remove protections for licensors in the future? Learn on the go with our new app. Although we have our requests decoupled, which is a good thing, there are still some issues. (instead of occupation of Japan, occupied Japan or Occupation-era Japan). A friendly maintainability testing relationship. Also check weve created factory function. Movie about robotic child seeking to wake his mother, How to help player quickly make a decision when they have no way of knowing which option is best, Laymen's description of "modals" to clients. This basically means that the factory used for this provider should return an Array of Functions where each Function should return a Promise. But for the simplicity, well call github api to get the user information here. Angular suspend the app initialization until all the funciton provided by the APP_INITALIZER are run. But before going to that lets check out the wrong place to store the configs. This is only because is easier to test.
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