apps/rxjs.dev/content/deprecations/breaking-changes.md
TS: RxJS requires TS 4.2
rxjs-compat: rxjs-compat is not published for v7
toPromise: toPromise return type now returns T | undefined in TypeScript, which is correct, but may break builds.
Subscription: add no longer returns an unnecessary Subscription reference. This was done to prevent confusion caused by a legacy behavior. You can now add and remove functions and Subscriptions as teardowns to and from a Subscription using add and remove directly. Before this, remove only accepted subscriptions.
Observable: lift no longer exposed. It was NEVER documented that end users of the library should be creating operators using lift. Lift has a variety of issues and was always an internal implementation detail of rxjs that might have been used by a few power users in the early days when it had the most value. The value of lift, originally, was that subclassed Observables would compose through all operators that implemented lift. The reality is that feature is not widely known, used, or supported, and it was never documented as it was very experimental when it was first added. Until the end of v7, lift will remain on Observable. Standard JavaScript users will notice no difference. However, TypeScript users might see complaints about lift not being a member of observable. To workaround this issue there are two things you can do: 1. Rewrite your operators as outlined in the documentation, such that they return new Observable. or 2. cast your observable as any and access lift that way. Method 1 is recommended if you do not want things to break when we move to version 8.
Subscriber: new Subscriber no longer takes 0-3 arguments. To create a Subscriber with 0-3 arguments, use Subscriber.create. However, please note that there is little to no reason that you should be creating Subscriber references directly, and Subscriber.create and new Subscriber are both deprecated.
onUnhandledError: Errors that occur during setup of an observable subscription after the subscription has emitted an error or completed will now throw in their own call stack. Before it would call console.warn. This is potentially breaking in edge cases for node applications, which may be configured to terminate for unhandled exceptions. In the unlikely event this affects you, you can configure the behavior to console.warn in the new configuration setting like so: import { config } from 'rxjs'; config.onUnhandledError = (err) => console.warn(err);
RxJS Error types Tests that are written with naive expectations against errors may fail now that errors have a proper stack property. In some testing frameworks, a deep equality check on two error instances will check the values in stack, which could be different.
unsubscribe no longer available via the this context of observer functions. To reenable, set config.useDeprecatedNextContext = true on the rxjs config found at import { config } from 'rxjs';. Note that enabling this will result in a performance penalty for all consumer subscriptions.
Leaked implementation detail _unsubscribeAndRecycle of Subscriber has been removed. Just use new Subscription objects
The static sortActions method on VirtualTimeScheduler is no longer publicly exposed by our TS types.
Notification.createNext(undefined) will no longer return the exact same reference every time.
Type signatures tightened up around Notification and dematerialize, may uncover issues with invalid types passed to those operators.
Experimental support for for await has been removed. Use https://github.com/benlesh/rxjs-for-await instead.
ReplaySubject no longer schedules emissions when a scheduler is provided. If you need that behavior,
please compose in observeOn using pipe, for example: new ReplaySubject(2, 3000).pipe(observeOn(asap))
rxjs-compat: rxjs/Rx is no longer a valid import site.
as.assource observable as a third argument to the predicate. That feature was rarely used, and of limited value. The workaround is to simply close over the source inside of the function if you need to access it in there.defer no longer allows factories to return void or undefined. All factories passed to defer must return a proper ObservableInput, such as Observable, Promise, et al. To get the same behavior as you may have relied on previously, return EMPTY or return of() from the factory.thisArg will now default to undefined. The previous default of MapSubscriber never made any sense. This will only affect code that calls map with a function and references this like so: source.pipe(map(function () { console.log(this); })). There wasn't anything useful about doing this, so the breakage is expected to be very minimal. If anything we're no longer leaking an implementation detail.mergeScan will no longer emit its inner state again upon completion.SchedulerLike may result in the wrong type which includes the SchedulerLike, even though the run time implementation does not support that. Developers should be using scheduled insteadpairs will no longer function in IE without a polyfill for Object.entries. pairs itself is also deprecated in favor of users just using from(Object.entries(obj)).race() will no longer subscribe to subsequent observables if a provided source synchronously errors or completes. This means side effects that might have occurred during subscription in those rare cases will no longer occur.repeat would result in an observable that repeats forever.retry would result in an observable that repeats forever.single operator will now throw for scenarios where values coming in are either not present, or do not match the provided predicate. Error types have thrown have also been updated, please check documentation for changes.skipLast will no longer error when passed a negative number, rather it will simply return the source, as though 0 was passed.startWith will return incorrect types when called with more than 7 arguments and a scheduler. Passing scheduler to startWith is deprecatedtake and will now throw runtime error for arguments that are negative or NaN, this includes non-TS calls like take().takeLast now has runtime assertions that throw TypeErrors for invalid arguments. Calling takeLast without arguments or with an argument that is NaN will throw a TypeErrorthrowError is no longer able to emit a function as an error directly. If you need to push a function as an error, you will have to use the factory function to return the function like so: throwError(() => functionToEmit), in other words throwError(() => () => console.log('called later')).timestamp operator accepts a TimestampProvider, which is any object with a now method
that returns a number. This means pulling in less code for the use of the timestamp operator. This may cause
issues with TestScheduler run mode. (see Issue here)zip: Zipping a single array will now have a different result. This is an extreme corner-case, because it is very unlikely that anyone would want to zip an array with nothing at all. The workaround would be to wrap the array in another array zip([[1,2,3]]). But again, that's pretty weird.
zip: zip operators will no longer iterate provided iterables "as needed", instead the iterables will be treated as push-streams just like they would be everywhere else in RxJS. This means that passing an endless iterable will result in the thread locking up, as it will endlessly try to read from that iterable. This puts us in-line with all other Rx implementations. To work around this, it is probably best to use map or some combination of map and zip. For example, zip(source$, iterator) could be source$.pipe(map(value => [value, iterator.next().value])).
ajax body serialization will now use default XHR behavior in all cases. If the body is a Blob, ArrayBuffer, any array buffer view (like a byte sequence, e.g. Uint8Array, etc), FormData, URLSearchParams, string, or ReadableStream, default handling is use. If the body is otherwise typeof "object", then it will be converted to JSON via JSON.stringify, and the Content-Type header will be set to application/json;charset=utf-8. All other types will emit an error.
The Content-Type header passed to ajax configuration no longer has any effect on the serialization behavior of the AJAX request.
For TypeScript users, AjaxRequest is no longer the type that should be explicitly used to create an ajax. It is now AjaxConfig, although the two types are compatible, only AjaxConfig has progressSubscriber and createXHR.
ajax: In an extreme corner-case... If an error occurs, the responseType is "json", we're in IE, and the responseType is not valid JSON, the ajax observable will no longer emit a syntax error, rather it will emit a full AjaxError with more details.
ajax: Ajax implementation drops support for IE10 and lower. This puts us in-line with other implementations and helps clean up code in this area