Add a defaultContext property on ApolloClient

.changeset/breezy-spiders-tap.md

@@ -0,0 +1,38 @@
+---
+"@apollo/client": patch
+---
+
+Add a `defaultContext` option and property on `ApolloClient`, e.g. for keeping track of changing auth tokens or dependency injection.
+
+This can be used e.g. in authentication scenarios, where a new token might be
+generated outside of the link chain and should passed into the link chain.
+
+```js
+import { ApolloClient, createHttpLink, InMemoryCache } from '@apollo/client';
+import { setContext } from '@apollo/client/link/context';
+
+const httpLink = createHttpLink({
+  uri: '/graphql',
+});
+
+const authLink = setContext((_, { headers, token }) => {
+  return {
+    headers: {
+      ...headers,
+      authorization: token ? `Bearer ${token}` : "",
+    }
+  }
+});
+
+const client = new ApolloClient({
+  link: authLink.concat(httpLink),
+  cache: new InMemoryCache()
+});
+
+// somewhere else in your application
+function onNewToken(newToken) {
+  // token can now be changed for future requests without need for a global
+  // variable, scoped ref or recreating the client
+  client.defaultContext.token = newToken
+}
+```

src/core/ApolloClient.ts

@@ -54,6 +54,7 @@ export type ApolloClientOptions<TCacheShape> = {
   connectToDevTools?: boolean;
   queryDeduplication?: boolean;
   defaultOptions?: DefaultOptions;
+  defaultContext?: Partial<DefaultContext>;
   assumeImmutableResults?: boolean;
   resolvers?: Resolvers | Resolvers[];
   typeDefs?: string | string[] | DocumentNode | DocumentNode[];
@@ -150,6 +151,7 @@ export class ApolloClient<TCacheShape> implements DataProxy {
         __DEV__,
       queryDeduplication = true,
       defaultOptions,
+      defaultContext,
       assumeImmutableResults = cache.assumeImmutableResults,
       resolvers,
       typeDefs,
@@ -199,6 +201,7 @@ export class ApolloClient<TCacheShape> implements DataProxy {
       cache: this.cache,
       link: this.link,
       defaultOptions: this.defaultOptions,
+      defaultContext,
       documentTransform,
       queryDeduplication,
       ssrMode,
@@ -692,4 +695,8 @@ export class ApolloClient<TCacheShape> implements DataProxy {
   public setLink(newLink: ApolloLink) {
     this.link = this.queryManager.link = newLink;
   }
+
+  public get defaultContext() {
+    return this.queryManager.defaultContext;
+  }
 }

src/core/QueryManager.ts

@@ -8,6 +8,7 @@ import { equal } from "@wry/equality";
 import type { ApolloLink, FetchResult } from "../link/core/index.js";
 import { execute } from "../link/core/index.js";
 import {
+  compact,
   hasDirectives,
   isExecutionPatchIncrementalResult,
   isExecutionPatchResult,
@@ -62,6 +63,7 @@ import type {
   InternalRefetchQueriesOptions,
   InternalRefetchQueriesResult,
   InternalRefetchQueriesMap,
+  DefaultContext,
 } from "./types.js";
 import { LocalState } from "./LocalState.js";
 
@@ -106,6 +108,7 @@ export class QueryManager<TStore> {
   public readonly assumeImmutableResults: boolean;
   public readonly documentTransform: DocumentTransform;
   public readonly ssrMode: boolean;
+  public readonly defaultContext: Partial<DefaultContext>;
 
   private queryDeduplication: boolean;
   private clientAwareness: Record<string, string> = {};
@@ -137,6 +140,7 @@ export class QueryManager<TStore> {
     clientAwareness = {},
     localState,
     assumeImmutableResults = !!cache.assumeImmutableResults,
+    defaultContext,
   }: {
     cache: ApolloCache<TStore>;
     link: ApolloLink;
@@ -148,6 +152,7 @@ export class QueryManager<TStore> {
     clientAwareness?: Record<string, string>;
     localState?: LocalState<TStore>;
     assumeImmutableResults?: boolean;
+    defaultContext?: Partial<DefaultContext>;
   }) {
     const defaultDocumentTransform = new DocumentTransform(
       (document) => this.cache.transformDocument(document),
@@ -172,6 +177,7 @@ export class QueryManager<TStore> {
           // selections and fragments from the fragment registry.
           .concat(defaultDocumentTransform)
       : defaultDocumentTransform;
+    this.defaultContext = defaultContext || Object.create(null);
 
     if ((this.onBroadcast = onBroadcast)) {
       this.mutationStore = Object.create(null);
@@ -1154,7 +1160,9 @@ export class QueryManager<TStore> {
     return asyncMap(
       this.getObservableFromLink(
         linkDocument,
-        options.context,
+        // explicitly a shallow merge so any class instances etc. a user might
+        // put in here will not be merged into each other.
+        compact(this.defaultContext, options.context),
         options.variables
       ),
 

src/core/__tests__/QueryManager/index.ts

@@ -6253,4 +6253,221 @@ describe("QueryManager", () => {
       }
     );
   });
+
+  describe("defaultContext", () => {
+    let _: any; // trash variable to throw away values when destructuring
+    _ = _; // omit "'_' is declared but its value is never read." compiler warning
+
+    it("ApolloClient and QueryManager share a `defaultContext` instance (default empty object)", () => {
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: ApolloLink.empty(),
+      });
+
+      expect(client.defaultContext).toBe(client["queryManager"].defaultContext);
+    });
+
+    it("ApolloClient and QueryManager share a `defaultContext` instance (provided option)", () => {
+      const defaultContext = {};
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: ApolloLink.empty(),
+        defaultContext,
+      });
+
+      expect(client.defaultContext).toBe(defaultContext);
+      expect(client["queryManager"].defaultContext).toBe(defaultContext);
+    });
+
+    it("`defaultContext` cannot be reassigned on the user-facing `ApolloClient`", () => {
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: ApolloLink.empty(),
+      });
+
+      expect(() => {
+        // @ts-ignore
+        client.defaultContext = { query: { fetchPolicy: "cache-only" } };
+      }).toThrowError(/Cannot set property defaultContext/);
+    });
+
+    it("`defaultContext` will be applied to the context of a query", async () => {
+      let context: any;
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: new ApolloLink(
+          (operation) =>
+            new Observable((observer) => {
+              ({ cache: _, ...context } = operation.getContext());
+              observer.complete();
+            })
+        ),
+        defaultContext: {
+          foo: "bar",
+        },
+      });
+
+      await client.query({
+        query: gql`
+          query {
+            foo
+          }
+        `,
+      });
+
+      expect(context.foo).toBe("bar");
+    });
+
+    it("`ApolloClient.defaultContext` can be modified and changes will show up in future queries", async () => {
+      let context: any;
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: new ApolloLink(
+          (operation) =>
+            new Observable((observer) => {
+              ({ cache: _, ...context } = operation.getContext());
+              observer.complete();
+            })
+        ),
+        defaultContext: {
+          foo: "bar",
+        },
+      });
+
+      // one query to "warm up" with an old value to make sure the value
+      // isn't locked in at the first query or something
+      await client.query({
+        query: gql`
+          query {
+            foo
+          }
+        `,
+      });
+
+      expect(context.foo).toBe("bar");
+
+      client.defaultContext.foo = "changed";
+
+      await client.query({
+        query: gql`
+          query {
+            foo
+          }
+        `,
+      });
+
+      expect(context.foo).toBe("changed");
+    });
+
+    it("`defaultContext` will be shallowly merged with explicit context", async () => {
+      let context: any;
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: new ApolloLink(
+          (operation) =>
+            new Observable((observer) => {
+              ({ cache: _, ...context } = operation.getContext());
+              observer.complete();
+            })
+        ),
+        defaultContext: {
+          foo: { bar: "baz" },
+          a: { b: "c" },
+        },
+      });
+
+      await client.query({
+        query: gql`
+          query {
+            foo
+          }
+        `,
+        context: {
+          a: { x: "y" },
+        },
+      });
+
+      expect(context).toEqual(
+        expect.objectContaining({
+          foo: { bar: "baz" },
+          a: { b: undefined, x: "y" },
+        })
+      );
+    });
+
+    it("`defaultContext` will be shallowly merged with context from `defaultOptions.query.context", async () => {
+      let context: any;
+      const client = new ApolloClient({
+        cache: new InMemoryCache(),
+        link: new ApolloLink(
+          (operation) =>
+            new Observable((observer) => {
+              ({ cache: _, ...context } = operation.getContext());
+              observer.complete();
+            })
+        ),
+        defaultContext: {
+          foo: { bar: "baz" },
+          a: { b: "c" },
+        },
+        defaultOptions: {
+          query: {
+            context: {
+              a: { x: "y" },
+            },
+          },
+        },
+      });
+
+      await client.query({
+        query: gql`
+          query {
+            foo
+          }
+        `,
+      });
+
+      expect(context.foo).toStrictEqual({ bar: "baz" });
+      expect(context.a).toStrictEqual({ x: "y" });
+    });
+
+    it(
+      "document existing behavior: `defaultOptions.query.context` will be " +
+        "completely overwritten by, not merged with, explicit context",
+      async () => {
+        let context: any;
+        const client = new ApolloClient({
+          cache: new InMemoryCache(),
+          link: new ApolloLink(
+            (operation) =>
+              new Observable((observer) => {
+                ({ cache: _, ...context } = operation.getContext());
+                observer.complete();
+              })
+          ),
+          defaultOptions: {
+            query: {
+              context: {
+                foo: { bar: "baz" },
+              },
+            },
+          },
+        });
+
+        await client.query({
+          query: gql`
+            query {
+              foo
+            }
+          `,
+          context: {
+            a: { x: "y" },
+          },
+        });
+
+        expect(context.a).toStrictEqual({ x: "y" });
+        expect(context.foo).toBeUndefined();
+      }
+    );
+  });
 });