fix(utils/selfDependent): prevent subject from being closed after unsub (#283)

Author: voliva

packages/utils/src/selfDependent.test.ts

@@ -6,6 +6,7 @@ import {
   takeWhile,
   switchMapTo,
   delay,
+  startWith,
 } from "rxjs/operators"
 import { TestScheduler } from "rxjs/testing"
 import { selfDependent } from "."
@@ -53,4 +54,64 @@ describe("selfDependent", () => {
       expectSubscriptions((source as any).subscriptions).toBe(sourceSub)
     })
   })
+
+  it("works after unsubscription and re-subscription", () => {
+    scheduler().run(({ expectObservable, cold }) => {
+      const source = cold("abcde")
+      const sourceSub1 = " ^--!"
+      const expected1 = "  abc"
+      const sourceSub2 = " -----^---!"
+      const expected2 = "  -----abcd"
+
+      const [lastValue$, connect] = selfDependent<string>()
+      const result$ = source.pipe(
+        withLatestFrom(lastValue$.pipe(startWith(""))),
+        map(([v]) => v),
+        connect(),
+      )
+
+      expectObservable(result$, sourceSub1).toBe(expected1)
+      expectObservable(result$, sourceSub2).toBe(expected2)
+    })
+  })
+
+  it("works after complete and re-subscription", () => {
+    scheduler().run(({ expectObservable, cold }) => {
+      const source = cold("abc|")
+      const sourceSub1 = " ^---!"
+      const expected1 = "  abc|"
+      const sourceSub2 = " -----^---!"
+      const expected2 = "  -----abc|"
+
+      const [lastValue$, connect] = selfDependent<string>()
+      const result$ = source.pipe(
+        withLatestFrom(lastValue$.pipe(startWith(""))),
+        map(([v]) => v),
+        connect(),
+      )
+
+      expectObservable(result$, sourceSub1).toBe(expected1)
+      expectObservable(result$, sourceSub2).toBe(expected2)
+    })
+  })
+
+  it("works after error and re-subscription", () => {
+    scheduler().run(({ expectObservable, cold }) => {
+      const source = cold("abc#")
+      const sourceSub1 = " ^---!"
+      const expected1 = "  abc#"
+      const sourceSub2 = " -----^---!"
+      const expected2 = "  -----abc#"
+
+      const [lastValue$, connect] = selfDependent<string>()
+      const result$ = source.pipe(
+        withLatestFrom(lastValue$.pipe(startWith(""))),
+        map(([v]) => v),
+        connect(),
+      )
+
+      expectObservable(result$, sourceSub1).toBe(expected1)
+      expectObservable(result$, sourceSub2).toBe(expected2)
+    })
+  })
 })

packages/utils/src/selfDependent.ts

@@ -1,5 +1,10 @@
-import { Observable, Subject, MonoTypeOperatorFunction } from "rxjs"
-import { tap } from "rxjs/operators"
+import {
+  Observable,
+  Subject,
+  MonoTypeOperatorFunction,
+  BehaviorSubject,
+} from "rxjs"
+import { switchAll, tap } from "rxjs/operators"
 
 /**
  * A creation operator that helps at creating observables that have circular
@@ -13,10 +18,23 @@ export const selfDependent = <T>(): [
   Observable<T>,
   () => MonoTypeOperatorFunction<T>,
 ] => {
-  const mirrored$ = new Subject<T>()
+  const activeSubject: BehaviorSubject<Subject<T>> = new BehaviorSubject(
+    new Subject<T>(),
+  )
   return [
-    mirrored$.asObservable(),
-    () => tap(mirrored$) as MonoTypeOperatorFunction<T>,
+    activeSubject.pipe(switchAll()),
+    () =>
+      tap({
+        next: (v) => activeSubject.value.next(v),
+        error: (e) => {
+          activeSubject.value.error(e)
+          activeSubject.next(new Subject<T>())
+        },
+        complete: () => {
+          activeSubject.value.complete()
+          activeSubject.next(new Subject<T>())
+        },
+      }) as MonoTypeOperatorFunction<T>,
   ]
 }