fix(subscriber): strict type signature for next method (#7172)

Author: raveclassic

package-lock.json

@@ -9,7 +9,7 @@ describe('SafeSubscriber', () => {
   it('should ignore next messages after unsubscription', () => {
     let times = 0;
 
-    const sub = new SafeSubscriber({
+    const sub = new SafeSubscriber<void>({
       next() { times += 1; }
     });
 
@@ -25,7 +25,7 @@ describe('SafeSubscriber', () => {
     let times = 0;
     let errorCalled = false;
 
-    const sub = new SafeSubscriber({
+    const sub = new SafeSubscriber<void>({
       next() { times += 1; },
       error() { errorCalled = true; }
     });
@@ -44,7 +44,7 @@ describe('SafeSubscriber', () => {
     let times = 0;
     let completeCalled = false;
 
-    const sub = new SafeSubscriber({
+    const sub = new SafeSubscriber<void>({
       next() { times += 1; },
       complete() { completeCalled = true; }
     });
@@ -268,4 +268,4 @@ describe('Subscriber', () => {
   } else {
     console.warn(`No support for FinalizationRegistry in Node ${process.version}`);
   }
-});
+});

spec/Subscriber-spec.ts

@@ -64,7 +64,7 @@ export class Subscriber<T> extends Subscription implements Observer<T> {
    * times.
    * @param value The `next` value.
    */
-  next(value?: T): void {
+  next(value: T): void {
     if (this.isStopped) {
       handleStoppedNotification(nextNotification(value), this);
     } else {
@@ -197,7 +197,7 @@ export class SafeSubscriber<T> extends Subscriber<T> {
       // The first argument is a function, not an observer. The next
       // two arguments *could* be observers, or they could be empty.
       partialObserver = {
-        next: (observerOrNext ?? undefined) as (((value: T) => void) | undefined),
+        next: (observerOrNext ?? undefined) as ((value: T) => void) | undefined,
         error: error ?? undefined,
         complete: complete ?? undefined,
       };