Angular wait for observable to complete

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Hi, I encountered this problem while using Http. I thought the third function is supposed to be called whatever happens success or error after the http request is finished, like. I'm on Angular 2 beta Tried using.

I have a question that I've been trying to search the Web for a while on. In my service, the http. Have they released a new version that has another way of "mapping" it or something? All I have is. You need rxJS for.

Would be very helpful if this is mentioned on the docs, so people would not confuse between using third callback or observer's finally. It's Angular's Http module that's not firing the third callback function.

I can't replicate this in beta. The observable specification says either. Closing this. So how come for Rxjs calls the complete one is never called, yet. Surely they should both be called if they are both meant to be a final callback to invoke?

The promise. Maybe it would be good to consider reopening this issue till we can find out if the missing complete callback is an intended implementation in Angular http Observables and why its missing? I agree trickpattyFH20I'd be interested to know if this was intentional because to me it seems like the. Complete and finally are totally different things. Complete means that the observable steam was finished successfully.

Because you can have many success calls. Finally means that steam has ended, either successfully or not. So, you might be getting multiple or no success calls, zero or one error call, zero or one complete and zero or one finally. I experienced this exact behavior today. Calling http. The complete callback was never being called. This ended up being an issue with an Http Interceptor library I was using. After removing this library and just using the standard HttpModule, the complete callback started working again.

If you're using any sort of wrapper or other interceptor functionality around Http, be mindful of this. Using a RESTful service, why wouldn't ng2's http use the complete functionality of rxjs?

Don't know if http completing was a recent development. DzmitryShylovich Sorry for the inconvenience then, has gotta be something else in our setup then. Without the return in the map would give me a TypeScript error on the : saying that a ; is expected.

Aleksandr-Leotech Ok.If you are building a RxJS Angular service layer for the first time, you will likely run into one of these scenarios in the first few services that you build. In this post, we will go over some common trouble situations, explain why the situation occurs and how to fix it. If you have used RxJs before, then try to guess the problem in each scenario, just for fun!

We have written our newest service method, all the data will be saved to the backend with one click of a button:. We will plug in a messages component and an error handling service later to show any error messages that might occur, but right now we will simply trigger the save operation via a click handler:. And there we have it, the Save functionality is implemented.

Except that when we try this out, try to guess what happens? Nothing happened :-! But the method is being called, or so we conclude after some debugging. So what's going on here? An observable itself is just a definition of a way to handle a stream of values.

We can think of it as something close to a function. Creating an observable is somewhat similar to declaring a function, the function itself is just a declaration. Calling the function is something entirely different, as defining a function does not execute its code. We need to call the function in order for something to happen, and that is also the case with an Observable: we need to subscribe to it in order for it to work!

Notice that now we are returning the Observable that we created, while before the Observable was created and the method returned without the Observable being subscribed to. In order to avoid the issue we need to ensure that we subscribe to the Observables that are returned by the HTTP service, either directly or via the async pipe.

Speaking of the async pipe, let's give it a try, and pass it in some observable that we get back from the service layer. The observable will emit a list of lessons:.

So we add a subscription to handle the error, and pass in the observable to the async pipe. So what could have gone wrong here? Nothing, so we try this out and everything is working.

But for whatever reason you decide to have a look at the network tab, as you usually leave the Dev Tools opened during development. That's right, duplicate HTTP requests! The request for reading the data is being issued twice. So what is going on here?

It turns out that as the Observable is just a definition, let's remember that in a sense its something close to a function declaration, if we subscribe to it multiple times this means that each time a new HTTP request will be issued, one for each subscription. And this not what we where trying to implement, we want to issue only one HTTP request, emit the data and handle errors if they occur otherwise print the data to the screen.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a method that needs to wait for an observable to finish.

I know observable are great for returning single pieces of data over time but I need to know when this observable has completely finished returning all of its data so I can run validation code on the object it has returned.

The method getCustom subscribes to an observable run on the supplied url which then returns the observable. I am not too sure if this is the best way to approach this situation so I would appreciate if anyone could give me any advice or a direction to handle this.

The heart of an observable data service is the RxJs Subject. Subjects implement both the Observer and the Observable interfaces, meaning that we can use them to both emit values and register subscriptors. The subject is nothing more than a traditional event bus, but much more powerful as it provides all the RxJs functional operators with it. But at its heart, we simply use it to subscribe just like a regular observable.

OR you can use Observable. Learn more. Waiting for an observable to finish Ask Question.

Angular wait for multiple Observable

Asked 3 years ago. Active 3 years ago. Viewed 17k times. You can't wait for an observable to finish. You can only subscribe and pass a callback to subscribe These two methods are both in different services, could you possibly give an example of what you mean?

angular wait for observable to complete

Then don't call subscribe in the service just return the observable return this. See also stackoverflow. Active Oldest Votes. But at its heart, we simply use it to subscribe just like a regular observable source: angular-university.I have recently faced an interesting issue in an Angular application. It was an e-commerce solution, where a user could change his currency. I was using a modified price pipe, which had a dependency on settings containing the currency symbol. Because settings could be changed by a user, I had to get them from the server.

The problem occurred when angular wanted to use the pipe before it loaded the settings. I had to make the app wait for settings before it rendered the page. The answer to this problem was creating a Route Guard. I did use them before - for checking if the user is logged in. It turned out they can also be used to make sure some data is fetched before you display a component. In simple words, Guard is a class implementing one of above methods.

Angular Router will delay rendering of the OrdersModule until the settings have been loaded.

angular wait for observable to complete

The UsersModule is caching the settings in a backing field so that the request is fired only once. This is just a one way you can use guards in your application. They might be useful in some other situations too:. I hope you found this post useful.

Have you used guards in your application? What was the purpose? Passionate software developer interested in Web Development. NET, Angular2, Architecture and security. Currently doing remote consulting. Menu Home Contact Archives. Route Guards The answer to this problem was creating a Route Guard.

Testing Asynchronous Code

The Router supports multiple kinds of guards: CanActivate to mediate navigation to a route. CanActivateChild to mediate navigation to a child route. CanDeactivate to mediate navigation away from the current route. Resolve to perform route data retrieval before route activation. CanLoad to mediate navigation to a feature module loaded asynchronously. Creating a Route Guard In simple words, Guard is a class implementing one of above methods.

Other use cases for Route Guards This is just a one way you can use guards in your application.

angular wait for observable to complete

Exceptionless - better logging for.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Already on GitHub? Sign in to your account. This is probably best classified as a Router feature request. I'll describe what it is, my thinking, and a use case. What it is: Currently, the V3 Router waits for an Observable to Complete before completing navigation. I would like for it to instead continue navigation after the first Observable item is returned.

My thinking: Currently the Resolve treats the Observable as a Promise, defeating the power of the Observable. This doesn't present a barrier with Angular's Http, where only one item is returned. But unless I misunderstand, the point of using an Observable in Http is to allow easy extension throughout Angular into a scenario where the data is actually a stream.

Use case: I have a live data feed from a remote server. I subscribe to a resource, rather than get it. When viewing this resource in a page, I only need one snapshot to complete navigation and display the component, but I would still like the updates bound to the view. Observables as first-class citizens in Angular2 are great for displaying "live data". Resolvers in Angular are also very nice for a few reasons. One is that I can be sure I have all my data before performing initialization.

This greatly simplifies my component initialization logic. It also simplifies managing built-in operations Angular performs, such as avoiding errors binding templates to properties on null models. But where live data comes in, the current Resolve behavior is difficult to make use of. If we suppose the live data stream never completes, we have to instead resolve, for example, to Observable.

Or I can go through extra steps for each of my Observables, to Observable. But that's not enough, because there's not a symmetric exit hook for resolve, that I see. So instead I have to do some extra magic, such as tear down resources I didn't initialize in the component.

Your thoughts are appreciated. I'll also be happy to contribute effort if someone with design authority confirms an approach. I've actually been bashing my head against the wall for the last two days over this exact thing.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project?

Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. I think reading config in a constructor is pretty common programming practice.

My use case is to fetch config from a server, and stick it into a service, and then inject this ConfigService into other services. I do not want to inject ConfigService into other stuff until it's fully constructed and ready to be used - in other words, until the asynchronous request to the server has completed and my ConfigService has all the values populated into it. I've seen quite a few other users trying to accomplish the same thing on Stackoverflow.

angular wait for observable to complete

This kludge is becoming the defacto way to do it, and SO answers are getting highly upvoted, and multiple articles are being published on other websites - all recommending a bug-prone method.

That's not good for the framework's reputation long term. It should be easy to do it "the right way", whatever that is. Other issues that would be well served by async providers: Having exactly this problem currently!

The problem is that some services are defined in other modules and imported into the app module, in which case they are initialized first. All the rest is waiting. FYI, there're indeed asynchronous DI support in the very alpha: In my case I am using Ngrx, and the Effects in a non-lazy-loaded feature module depend on services which in turn try to retrieve the backend URL from the ConfigService in their constructors.

In my experience it is particularly a problem when using Ngrx Effects. As the plunkr demonstrates there may be other ways to reproduce the problem, but at least when using Effects I haven't found a way to solve the problem via structural changes.

There are workarounds, of course. One is to dynamically grab the values on every service method call.All applications have some amount of asynchronous code. Imagine if you had to wait for every application on your computer to complete a task before you could do something else. What if you had to wait for all the posts to load on Facebook before you could see your Facebook home page.

That's just not how the internet works. Everything is asynchronous. Google Analytics is asynchronously tracking your every move as you read this article Blocking is the opposite of async.

If you had blocking code, that would mean that every line of code has to wait for the previous line of code to finish executing. Let's take a quick detour to understand how concurrency works in JavaScript.

This will help us figure out why JavaScript is a single-thread language and yet async.

async / await in JavaScript - What, Why and How - Fun Fun Function

The heap is an area of unstructured memory. If you're familiar with memory allocation, you probably know what the heap does. The call stack is what we are referring to when we talk about the single thread.

Angular + Observable Example

This is our code that is executed by the browser. If we put any code in the call stack that takes too much time, we block the code execution and cause the page to freeze. But operations like timeouts and API calls would cause our application to freeze till they aren't complete.

That's why we don't need to worry about blocking code when we use a timeout. A perfect place to experiment with and see how these different elements come together is Loupe. Loupe allows you to see the runtime elements while the sample code is running. The timeout doesn't occur on the main call stack. But what happens when the 5 seconds get over. The WebAPI cannot push the log function straight to the main call stack.

That would cause all kinds of problems with functions being executed in an unpredictable order. Instead, the WebAPI queues the functions that need to run next in the callback queue.

The callback queue waits for the functions on the call stack to finish executing and then pushes it's next function into the call stack. In this manner, if you had multiple callbacks waiting to be fired, they'd all wait in the callback queue before being sent to the call stack for execution.

Now that you understand how basic async works in JavaScript let's see how we can use this to our advantage.


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