Fixes #11849, BatchHttpLink not monitoring friendly

.changeset/late-days-give.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Fixes [#11849](https://github.com/apollographql/apollo-client/issues/11849) by reevaluating `window.fetch` each time `BatchHttpLink` uses it, if not configured via `options.fetch`. Takes the same approach as PR [#8603](https://github.com/apollographql/apollo-client/pull/8603) which fixed the same issue in `HttpLink`.

src/link/batch-http/__tests__/batchHttpLink.ts

@@ -6,6 +6,7 @@ import { ApolloLink } from "../../core/ApolloLink";
 import { execute } from "../../core/execute";
 import {
   Observable,
+  ObservableSubscription,
   Observer,
 } from "../../../utilities/observables/Observable";
 import { BatchHttpLink } from "../batchHttpLink";
@@ -271,6 +272,8 @@ const createHttpLink = (httpArgs?: any) => {
   return new BatchHttpLink(args);
 };
 
+const subscriptions = new Set<ObservableSubscription>();
+
 describe("SharedHttpTest", () => {
   const data = { data: { hello: "world" } };
   const data2 = { data: { hello: "everyone" } };
@@ -300,10 +303,16 @@ describe("SharedHttpTest", () => {
       error,
       complete,
     };
+    subscriptions.clear();
   });
 
   afterEach(() => {
     fetchMock.restore();
+    if (subscriptions.size) {
+      // Tests within this describe block can add subscriptions to this Set
+      // that they want to be canceled/unsubscribed after the test finishes.
+      subscriptions.forEach((sub) => sub.unsubscribe());
+    }
   });
 
   it("raises warning if called with concat", () => {
@@ -624,6 +633,61 @@ describe("SharedHttpTest", () => {
     );
   });
 
+  it("uses the latest window.fetch function if options.fetch not configured", (done) => {
+    const httpLink = createHttpLink({ uri: "data" });
+
+    const fetch = window.fetch;
+    expect(typeof fetch).toBe("function");
+
+    const fetchSpy = jest.spyOn(window, "fetch");
+    fetchSpy.mockImplementation(() =>
+      Promise.resolve<Response>({
+        text() {
+          return Promise.resolve(
+            JSON.stringify({
+              data: { hello: "from spy" },
+            })
+          );
+        },
+      } as Response)
+    );
+
+    const spyFn = window.fetch;
+    expect(spyFn).not.toBe(fetch);
+
+    subscriptions.add(
+      execute(httpLink, {
+        query: sampleQuery,
+      }).subscribe({
+        error: done.fail,
+
+        next(result) {
+          expect(fetchSpy).toHaveBeenCalledTimes(1);
+          expect(result).toEqual({
+            data: { hello: "from spy" },
+          });
+
+          fetchSpy.mockRestore();
+          expect(window.fetch).toBe(fetch);
+
+          subscriptions.add(
+            execute(httpLink, {
+              query: sampleQuery,
+            }).subscribe({
+              error: done.fail,
+              next(result) {
+                expect(result).toEqual({
+                  data: { hello: "world" },
+                });
+                done();
+              },
+            })
+          );
+        },
+      })
+    );
+  });
+
   itAsync(
     "prioritizes context headers over setup headers",
     (resolve, reject) => {

src/link/batch-http/batchHttpLink.ts

@@ -3,6 +3,7 @@ import { ApolloLink } from "../core/index.js";
 import {
   Observable,
   hasDirectives,
+  maybe,
   removeClientSetsFromDocument,
 } from "../../utilities/index.js";
 import { fromError } from "../utils/index.js";
@@ -27,6 +28,8 @@ export namespace BatchHttpLink {
     Omit<HttpOptions, "useGETForQueries">;
 }
 
+const backupFetch = maybe(() => fetch);
+
 /**
  * Transforms Operation for into HTTP results.
  * context can include the headers property, which will be passed to the fetch function
@@ -43,7 +46,7 @@ export class BatchHttpLink extends ApolloLink {
     let {
       uri = "/graphql",
       // use default global fetch if nothing is passed in
-      fetch: fetcher,
+      fetch: preferredFetch,
       print = defaultPrinter,
       includeExtensions,
       preserveHeaderCase,
@@ -55,14 +58,10 @@ export class BatchHttpLink extends ApolloLink {
       ...requestOptions
     } = fetchParams || ({} as BatchHttpLink.Options);
 
-    // dev warnings to ensure fetch is present
-    checkFetcher(fetcher);
-
-    //fetcher is set here rather than the destructuring to ensure fetch is
-    //declared before referencing it. Reference in the destructuring would cause
-    //a ReferenceError
-    if (!fetcher) {
-      fetcher = fetch;
+    if (__DEV__) {
+      // Make sure at least one of preferredFetch, window.fetch, or backupFetch
+      // is defined, so requests won't fail at runtime.
+      checkFetcher(preferredFetch || backupFetch);
     }
 
     const linkConfig = {
@@ -163,7 +162,16 @@ export class BatchHttpLink extends ApolloLink {
       }
 
       return new Observable<FetchResult[]>((observer) => {
-        fetcher!(chosenURI, options)
+        // Prefer BatchHttpLink.Options.fetch (preferredFetch) if provided, and
+        // otherwise fall back to the *current* global window.fetch function
+        // (see issue #7832), or (if all else fails) the backupFetch function we
+        // saved when this module was first evaluated. This last option protects
+        // against the removal of window.fetch, which is unlikely but not
+        // impossible.
+        const currentFetch =
+          preferredFetch || maybe(() => fetch) || backupFetch;
+
+        currentFetch!(chosenURI, options)
           .then((response) => {
             // Make the raw response available in the context.
             operations.forEach((operation) =>