@rxjs/observable-polyfill

Conditional fallback for the web-platform Observable and Subscriber contracts used by RxJS 9.

npm install @rxjs/observable-polyfill@next

import '@rxjs/observable-polyfill';

The package preserves an existing callable globalThis.Observable. When the realm has no implementation, it installs the RxJS fallback together with its paired Subscriber and supported platform methods. It does not probe a native implementation for conformance, replace it, or make the platform Observable behave like an RxJS 7 cold Observable.

Use getObservablePolyfillInfo() when diagnostics need to distinguish the RxJS fallback from a native or foreign constructor:

import { getObservablePolyfillInfo } from '@rxjs/observable-polyfill';

console.log(getObservablePolyfillInfo()); // metadata for the RxJS fallback, or undefined

Cancellation and teardown use AbortSignal and Subscriber lifecycle. The package also conditionally supplies the supported EventTarget.when() surface without replacing an existing callable implementation.

The package requires Node 22.13+ and publishes one ESM implementation for browser, Webpack, import, and Node require(esm) resolution. Observable WPT is pinned at an exact upstream revision under test/wpt; the strict gate requires complete results and exact RxJS bundle identity in every fallback realm.

This package is the platform layer. RxJS operators and intentional producer-per-subscription primitives belong to the rxjs package.