angular 2+ http error handling

Question

I have this question here on how Angular2+ Observable handle Http errors. When we use Angular2+ Http APIs to make requests, if the response back has error status code, and error will be thrown.

In the Angular2 Official Starter project, the error handler function to be called in:

someObs.catch(handler)

In the handler, it actually returns:

Observable.throw(...)

My question is, wouldn't this thrown new error that could potentially crash the web app? Since in Javascript if you throw some error, the web app could then unexpected behaviours.

My understanding of Observable.catch is that when some error happens, we catch it we do something else(instead of throw a new error). And since the

Observable.catch

still requires us to return an Observable, would it be a best solution to return:

Observable.empty()

as it would not emit any new value so that subscribers won't react

cartant · Accepted Answer · 2017-07-12 05:04:38Z

1

If you are able to handle a particular error inside catch, you can return an observable that is used to continue the observable chain. Returning Observable.empty() might make sense - depending upon the situation.

If you cannot handle the caught error and you return Observable.empty, you've swallowed the error - which is, generally speaking, not a great idea (especially if the catch handler does not include some sort of reporting mechanism). Instead, re-throwing the error - or returning Observable.throw - gives the subscriber the opportunity to handle or report the error.

If the subscriber does not handle the error, what happens depends on the runtime. In the browser, the application won't crash due to the error being unhandled; it'll just be reported as an unhandled error - much the same as an unhandled promise rejection or an uncaught thrown error. In Node, it will fail fast/crash by default.

edited Jul 12, 2017 at 5:04

answered Jul 12, 2017 at 2:51

cartant

58.6k17 gold badges169 silver badges201 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Marlon Ou Over a year ago

I kinda get it know. It's like the observable sees the error, but not sure how to handle it and so pass it to the subscriber. Or it maybe that the catch clause parse random errors into a agreed-format in the app, and then let the subscriber process it.

Marlon Ou Over a year ago

But sometimes when I let an observable error to be thrown, the application does produce unexpected behaviours: in my case, the buttons and inputs still work(can still click or enter), but the javascript handlers no longer respond

Vamshi Over a year ago

I always make it a point to handle errors in component alone, so that I know what I can do when things go wrong. In different scenarios we want to do different things

Anna Over a year ago

also, you can create a global error handler to handle somehow the errors, which you didn't handle in your services/components. Here's an article on it medium.com/@amcdnl/…

Collectives™ on Stack Overflow

angular 2+ http error handling

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related