Improve createInput types and behavior

src/createInput.ts

@@ -1,9 +1,17 @@
 import { Subject, Observable, ReplaySubject } from "rxjs"
-import { finalize } from "rxjs/operators"
 import { distinctShareReplay } from "./operators/distinct-share-replay"
 
+interface CreateInput {
+  (): [(key: string) => Observable<void>, (key: string) => void]
+  <T>(defaultValue?: T): [
+    (key: string) => Observable<T>,
+    (key: string, update: T | ((prev: T) => T)) => void,
+  ]
+}
+
 const empty = Symbol("empty") as any
-export function createInput<T>(defaultValue: T = empty) {
+const F = () => false
+const createInput_ = <T>(defaultValue: T = empty) => {
   const cache = new Map<string, [Subject<T>, { latest: T }, Observable<T>]>()
   const getEntry = (key: string) => {
     let result = cache.get(key)
@@ -13,10 +21,9 @@ export function createInput<T>(defaultValue: T = empty) {
     if (defaultValue !== empty) {
       subject.next((current.latest = defaultValue))
     }
-    const source = subject.pipe(
-      finalize(() => cache.delete(key)),
-      distinctShareReplay(),
-    )
+    const source = distinctShareReplay(F, () => cache.delete(key))(
+      subject,
+    ) as Observable<T>
     result = [subject, current, source]
     cache.set(key, result)
     return result
@@ -31,3 +38,5 @@ export function createInput<T>(defaultValue: T = empty) {
   const getSource = (key: string) => getEntry(key)[2]
   return [getSource, onChange] as const
 }
+
+export const createInput = createInput_ as CreateInput

test/createInput.test.ts

@@ -1,4 +1,5 @@
 import { createInput } from "../src"
+import { scan } from "rxjs/operators"
 
 describe("createInput", () => {
   test("it returns the default value", () => {
@@ -21,6 +22,28 @@ describe("createInput", () => {
     sub.unsubscribe()
   })
 
+  test("it accepts void inputs", () => {
+    const [getClicks$, onClick] = createInput()
+
+    let latestValue: number | undefined = undefined
+    const sub = getClicks$("foo")
+      .pipe(scan(prev => prev + 1, 0))
+      .subscribe(x => {
+        latestValue = x
+      })
+
+    expect(latestValue).toBe(undefined)
+
+    onClick("foo")
+    onClick("foo")
+    onClick("foo")
+    onClick("foo")
+
+    expect(latestValue).toBe(4)
+
+    sub.unsubscribe()
+  })
+
   test("it replays the latest value to new subscriptions", () => {
     const [getCounter, setCounter] = createInput(10)
     const sub1 = getCounter("foo").subscribe()
@@ -53,27 +76,6 @@ describe("createInput", () => {
     sub3.unsubscribe()
   })
 
-  test("it does not trigger updates if the value has not changed", () => {
-    const [getCounter, setCounter] = createInput(10)
-
-    let nUpdates = 0
-    const sub1 = getCounter("foo").subscribe(() => {
-      nUpdates += 1
-    })
-    expect(nUpdates).toBe(1)
-
-    setCounter("foo", 100)
-    expect(nUpdates).toBe(2)
-
-    setCounter("foo", 100)
-    expect(nUpdates).toBe(2)
-
-    setCounter("foo", 100)
-    expect(nUpdates).toBe(2)
-
-    sub1.unsubscribe()
-  })
-
   test("the setter can also be a function", () => {
     const [getCounter, setCounter] = createInput(10)
 
@@ -94,10 +96,6 @@ describe("createInput", () => {
     expect(nUpdates).toBe(3)
     expect(latestValue).toBe(40)
 
-    setCounter("foo", x => x)
-    expect(nUpdates).toBe(3)
-    expect(latestValue).toBe(40)
-
     sub1.unsubscribe()
   })
 })