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perf(SafeSubscriber): avoid using Object.create #5646

Merged
merged 2 commits into from
Aug 25, 2020
Merged

perf(SafeSubscriber): avoid using Object.create #5646

merged 2 commits into from
Aug 25, 2020

Commits on Aug 24, 2020

  1. perf(SafeSubscriber): avoid using Object.create 

    In profiling sessions, the `SafeSubscriber` constructor was showing as hot
function for code that creates and tear downs Observables very frequently.
The usage of `Object.create` attributes to the slowness; avoiding using it
completely removes any overhead of `SafeSubscriber`.

The `Object.create` result was used to call anonymous subscribers in their
own context, i.e. the `this` pointer in `next`/`error`/`complete` is the
anonymous object itself. This commit implements an alternative to achieve
the same effect; binding the subscriber functions to the observer object.
    @JoostK @benlesh
    JoostK authored and benlesh committed Aug 24, 2020
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  2. feat(useDeprecatedNextContext): Puts deprecated next context behavior… 

    … behind a flag

- Adds a flag to `import { config } from 'rxjs';` that allows users to use the undocumented feature that gives access to `unsubscribe` via the `this` context of a `next` handler passed as part of an observer object to `subscribe`. This behavior is deprecated because it has very bad performance implications on all subscriptions and is relatively unused, definitely undocumented, and certainly mostly unknown.
- Adds a flag to silence console warn messages that are emitted when "bad" configuration settings are used.
- Adds some documentation.
- Adds tests.

BREAKING CHANGE: `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.
    @benlesh
    benlesh committed Aug 24, 2020
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