Stop using nested observables

Using nested subscriptions in Angular can lead to a number of problems, including:

Subscription leaks: Nested subscriptions can lead to subscription leaks, where subscriptions are not properly unsubscribed when a component is destroyed. This can cause memory leaks and potentially impact performance.

Poor readability: Nested subscriptions can make code harder to read and understand, especially when dealing with multiple levels of nesting. This can make it harder to debug and maintain code over time.

Error handling: Nested subscriptions can make it more difficult to handle errors, especially when dealing with multiple levels of nesting. This can make it harder to write code that gracefully handles errors and provides a good user experience.

To avoid these problems, it's generally recommended to use operators like switchMap or mergeMap to flatten nested observables into a single stream. This can make code more readable and easier to understand, while also avoiding the potential for subscription leaks and making it easier to handle errors.

Using these operators also enables better error handling. With a nested subscription, errors in inner subscription won't be propagated up the chain, making it harder to handle those errors. But with switchMap or mergeMap, any errors from the inner observable can be caught in the same .subscribe() call, allowing you to handle the errors appropriately.

By using observables and operators like switchMap or mergeMap, you can write code that is more efficient, easier to read and maintain, and provides a better user experience.