@apollo/client/CHANGELOG.md

A fully-featured caching GraphQL client.

# @apollo/client

## 4.1.3

### Patch Changes

- [#13111](https://github.com/apollographql/apollo-client/pull/13111) [`bf46fe0`](https://github.com/apollographql/apollo-client/commit/bf46fe019b316ea8a87a05981a89fac5411260b4) Thanks [@RogerHYang](https://github.com/RogerHYang)! - Fix `createFetchMultipartSubscription` to support cancellation via `AbortController`

  Previously, calling `dispose()` or `unsubscribe()` on a subscription created by `createFetchMultipartSubscription` had no effect - the underlying fetch request would continue running until completion. This was because no `AbortController` was created or passed to `fetch()`, and no cleanup function was returned from the Observable.

## 4.1.2

### Patch Changes

- [#13105](https://github.com/apollographql/apollo-client/pull/13105) [`8b62263`](https://github.com/apollographql/apollo-client/commit/8b62263e19b3442e20fea822de62074cf4f5cb22) Thanks [@phryneas](https://github.com/phryneas)! - `ssrMode`, `ssrForceFetchDelay` or `prioritizeCacheValues` should not override `fetchPolicy: 'cache-only'`, `fetchPolicy: 'no-cache'`, `fetchPolicy: 'standby'`, `skip: true`, or `skipToken` when reading the initial value of an `ObservableQuery`.

- [#13105](https://github.com/apollographql/apollo-client/pull/13105) [`8b62263`](https://github.com/apollographql/apollo-client/commit/8b62263e19b3442e20fea822de62074cf4f5cb22) Thanks [@phryneas](https://github.com/phryneas)! - Fix `skipToken` in `useQuery` with `prerenderStatic` and related SSR functions.

- [#13105](https://github.com/apollographql/apollo-client/pull/13105) [`8b62263`](https://github.com/apollographql/apollo-client/commit/8b62263e19b3442e20fea822de62074cf4f5cb22) Thanks [@phryneas](https://github.com/phryneas)! - Avoid fetches with `fetchPolicy: no-cache` in `useQuery` with `prerenderStatic` and related SSR functions.

## 4.1.1

### Patch Changes

- [#13103](https://github.com/apollographql/apollo-client/pull/13103) [`dee7dcf`](https://github.com/apollographql/apollo-client/commit/dee7dcff4d4baa26d623d1ecace60be88c684c1a) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure `@client` fields that are children of aliased server fields are resolved correctly.

## 4.1.0

### Minor Changes

- [#13043](https://github.com/apollographql/apollo-client/pull/13043) [`65e66ca`](https://github.com/apollographql/apollo-client/commit/65e66cafb6828b63d14b64877bbad47af95f66e4) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Support `headers` transport for enhanced client awareness.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`785e223`](https://github.com/apollographql/apollo-client/commit/785e2232b4f7d9e561611cd4f45b8fdd1e44319e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - You can now provide a callback function as the `context` option on the `mutate` function returned by `useMutation`. The callback function is called with the value of the `context` option provided to the `useMutation` hook. This is useful if you'd like to merge the context object provided to the `useMutation` hook with a value provided to the `mutate` function.

  ```ts
  function MyComponent() {
    const [mutate, result] = useMutation(MUTATION, {
      context: { foo: true },
    });

    async function runMutation() {
      await mutate({
        // sends context as { foo: true, bar: true }
        context: (hookContext) => ({ ...hookContext, bar: true }),
      });
    }

    // ...
  }
  ```

- [#12923](https://github.com/apollographql/apollo-client/pull/12923) [`94ea3e3`](https://github.com/apollographql/apollo-client/commit/94ea3e32c82dd767b62a6907be6c3891864633af) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where deferred payloads that returned arrays with fewer items than the original cached array would retain items from the cached array. This change includes `@stream` arrays where stream arrays replace the cached arrays.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`96b531f`](https://github.com/apollographql/apollo-client/commit/96b531f6b57a158aa2c57da976c6dd22c1a7f4d5) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Don't set the fallback value of a `@client` field to `null` when a `read` function is defined. Instead the `read` function will be called with an `existing` value of `undefined` to allow default arguments to be used to set the returned value.

  When a `read` function is not defined nor is there a defined resolver for the field, warn and set the value to `null` only in that instance.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`45ebb52`](https://github.com/apollographql/apollo-client/commit/45ebb52bcb84b81ce3a066204456c2e20f3d4c98) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for `from: null` in `client.watchFragment` and `cache.watchFragment`. When `from` is `null`, the emitted result is:

  ```ts
  {
    data: null,
    dataState: "complete",
    complete: true,
  }
  ```

- [#12926](https://github.com/apollographql/apollo-client/pull/12926) [`2b7f2c1`](https://github.com/apollographql/apollo-client/commit/2b7f2c167fc4a94e06457777f0c57b6dac7b2f2f) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Support the newer incremental delivery format for the `@defer` directive implemented in `graphql@17.0.0-alpha.9`. Import the `GraphQL17Alpha9Handler` to use the newer incremental delivery format with `@defer`.

  ```ts
  import { GraphQL17Alpha9Handler } from "@apollo/client/incremental";

  const client = new ApolloClient({
    // ...
    incrementalHandler: new GraphQL17Alpha9Handler(),
  });
  ```

  > [!NOTE]
  > In order to use the `GraphQL17Alpha9Handler`, the GraphQL server MUST implement the newer incremental delivery format. You may see errors or unusual behavior if you use the wrong handler. If you are using Apollo Router, continue to use the `Defer20220824Handler` because Apollo Router does not yet support the newer incremental delivery format.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`45ebb52`](https://github.com/apollographql/apollo-client/commit/45ebb52bcb84b81ce3a066204456c2e20f3d4c98) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for arrays with `useFragment`, `useSuspenseFragment`, and `client.watchFragment`. This allows the ability to use a fragment to watch multiple entities in the cache. Passing an array to `from` will return `data` as an array where each array index corresponds to the index in the `from` array.

  ```ts
  function MyComponent() {
    const result = useFragment({
      fragment,
      from: [item1, item2, item3],
    });

    // `data` is an array with 3 items
    console.log(result); // { data: [{...}, {...}, {...}], dataState: "complete", complete: true }
  }
  ```

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`45ebb52`](https://github.com/apollographql/apollo-client/commit/45ebb52bcb84b81ce3a066204456c2e20f3d4c98) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add a `getCurrentResult` function to the observable returned by `client.watchFragment` and `cache.watchFragment` that returns the current value for the watched fragment.

  ```ts
  const observable = client.watchFragment({
    fragment,
    from: { __typename: "Item", id: 1 },
  });

  console.log(observable.getCurrentResult());
  // {
  //   data: {...},
  //   dataState: "complete",
  //   complete: true,
  // }
  ```

- [#13038](https://github.com/apollographql/apollo-client/pull/13038) [`109efe7`](https://github.com/apollographql/apollo-client/commit/109efe7e4380b579c6a577982bd9a6e8c6a53892) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add the `from` option to `readFragment`, `watchFragment`, and `updateFragment`.

- [#12918](https://github.com/apollographql/apollo-client/pull/12918) [`2e224b9`](https://github.com/apollographql/apollo-client/commit/2e224b99894432822f926fdfec36bd46dd73b35e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for the `@stream` directive on both the `Defer20220824Handler` and the `GraphQL17Alpha2Handler`.

  > [!NOTE]
  > The implementations of `@stream` differ in the delivery of incremental results between the different GraphQL spec versions. If you upgrading from the older format to the newer format, expect the timing of some incremental results to change.

- [#13056](https://github.com/apollographql/apollo-client/pull/13056) [`b224efc`](https://github.com/apollographql/apollo-client/commit/b224efc25515370c68b514405762e68a443e4a4a) Thanks [@jerelmiller](https://github.com/jerelmiller)! - `InMemoryCache` no longer filters out explicitly returned `undefined` items from `read` functions for array fields. This now makes it possible to create `read` functions on array fields that return partial data and trigger a fetch for the full list.

- [#13058](https://github.com/apollographql/apollo-client/pull/13058) [`121a2cb`](https://github.com/apollographql/apollo-client/commit/121a2cb68820727186ecd74ce1041ef95284682e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add an `extensions` option to `cache.write`, `cache.writeQuery`, and `client.writeQuery`. This makes `extensions` available in cache `merge` functions which can be accessed with the other merge function options.

  As a result of this change, any `extensions` returned in GraphQL operations are now available in `merge` in the cache writes for these operations.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`96b531f`](https://github.com/apollographql/apollo-client/commit/96b531f6b57a158aa2c57da976c6dd22c1a7f4d5) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add an abstract `resolvesClientField` function to `ApolloCache` that can be used by caches to tell `LocalState` if it can resolve a `@client` field when a local resolver is not defined.

  `LocalState` will emit a warning and set a fallback value of `null` when no local resolver is defined and `resolvesClientField` returns `false`, or isn't defined. Returning `true` from `resolvesClientField` signals that a mechanism in the cache will set the field value. In this case, `LocalState` won't set the field value.

- [#13078](https://github.com/apollographql/apollo-client/pull/13078) [`bf1e0dc`](https://github.com/apollographql/apollo-client/commit/bf1e0dcb2f6c9b94576dc6d049745f1869cd0043) Thanks [@phryneas](https://github.com/phryneas)! - Use the default stream merge function for `@stream` fields only if stream info is present. This change means that using the older `Defer20220824Handler` will not use the default stream merge function and will instead truncate the streamed array on the first chunk.

### Patch Changes

- [#12884](https://github.com/apollographql/apollo-client/pull/12884) [`d329790`](https://github.com/apollographql/apollo-client/commit/d32979070381f1897c90fb276e25a0c8375cc29a) Thanks [@phryneas](https://github.com/phryneas)! - Ensure that `PreloadedQueryRef` instances are unsubscribed when garbage collected

- [#13086](https://github.com/apollographql/apollo-client/pull/13086) [`1a1d408`](https://github.com/apollographql/apollo-client/commit/1a1d4088f549088d4af3ff1f2d08d1c8e9af2a4d) Thanks [@phryneas](https://github.com/phryneas)! - Change the returned value from `null` to `{}` when all fields in a query were skipped.

  This also fixes a bug where `useSuspenseQuery` would suspend indefinitely when all fields were skipped.

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where errors parsed from incremental chunks in `ErrorLink` might throw when using the `GraphQL17Alpha9Handler`.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`45ebb52`](https://github.com/apollographql/apollo-client/commit/45ebb52bcb84b81ce3a066204456c2e20f3d4c98) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Deduplicate watches created by `useFragment`, `client.watchFragment`, and `cache.watchFragment` that contain the same fragment, variables, and identifier. This should improve performance in situations where a `useFragment` or a `client.watchFragment` is used to watch the same object in multiple places of an application.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`259ae9b`](https://github.com/apollographql/apollo-client/commit/259ae9bafaa8122996b0a52dd99828b2261087e5) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Allow `FragmentType` not only to be called as `FragmentType<TData>`, but also as `FragmentType<TypedDocumentNode>`.

- [#12925](https://github.com/apollographql/apollo-client/pull/12925) [`5851800`](https://github.com/apollographql/apollo-client/commit/58518000edebb2a4b75c36ed22e9b67b3a254fa0) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where calling `fetchMore` with `@defer` or `@stream` would not rerender incremental results as they were streamed.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`9e55188`](https://github.com/apollographql/apollo-client/commit/9e55188adcb4cf4236b14eb552286a4505650a29) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Truncate `@stream` arrays only on last chunk by default.

- [#13083](https://github.com/apollographql/apollo-client/pull/13083) [`f3c2be1`](https://github.com/apollographql/apollo-client/commit/f3c2be1665d8e2e260a4f55ec803d6e609748390) Thanks [@phryneas](https://github.com/phryneas)! - Expose the `ExtensionsWithStreamInfo` type for `extensions` in `Cache.writeQuery`, `Cache.write` and `Cache.update` so other cache implementations also can correctly access them.

- [#12923](https://github.com/apollographql/apollo-client/pull/12923) [`94ea3e3`](https://github.com/apollographql/apollo-client/commit/94ea3e32c82dd767b62a6907be6c3891864633af) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Improve the cache data loss warning message when `existing` or `incoming` is an array.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`4631175`](https://github.com/apollographql/apollo-client/commit/46311758f703ec7baa9013a49b897e823fd4edb0) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ignore top-level `data` values on subsequent chunks in incremental responses.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`2be8de2`](https://github.com/apollographql/apollo-client/commit/2be8de26f1bb68d2d6cd0d286565d47455332b47) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Create mechanism to add experimental features to Apollo Client

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`96b531f`](https://github.com/apollographql/apollo-client/commit/96b531f6b57a158aa2c57da976c6dd22c1a7f4d5) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure `LocalState` doesn't try to read from the cache when using a `no-cache` fetch policy.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`bb8ed7b`](https://github.com/apollographql/apollo-client/commit/bb8ed7b6b7e36e313822e44b230e27031d6fcbd9) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure an error is thrown when `@stream` is detected and an `incrementalDelivery` handler is not configured.

- [#13053](https://github.com/apollographql/apollo-client/pull/13053) [`23ca0ba`](https://github.com/apollographql/apollo-client/commit/23ca0ba895473b397805e6bcc70e0fcf987547c5) Thanks [@phryneas](https://github.com/phryneas)! - Use memoized observable mapping when using `watchFragment`, `useFragment` or `useSuspenseFragment`.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`44706a2`](https://github.com/apollographql/apollo-client/commit/44706a2e7ae2c977fa917214a1ff5e5fe4a9b3a7) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add helper type `QueryRef.ForQuery<TypedDocumentNode>`

- [#13082](https://github.com/apollographql/apollo-client/pull/13082) [`c257418`](https://github.com/apollographql/apollo-client/commit/c2574181f6b0d9ae059dfa3822a7842ec5f8ff1f) Thanks [@phryneas](https://github.com/phryneas)! - Pass `streamInfo` through result extensions as a `WeakRef`.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`4631175`](https://github.com/apollographql/apollo-client/commit/46311758f703ec7baa9013a49b897e823fd4edb0) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix the `Defer20220824Handler.SubsequentResult` type to match the `FormattedSubsequentIncrementalExecutionResult` type in `graphql@17.0.0-alpha.2`.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`96b531f`](https://github.com/apollographql/apollo-client/commit/96b531f6b57a158aa2c57da976c6dd22c1a7f4d5) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Warn when using a `no-cache` fetch policy without a local resolver defined. `no-cache` queries do not read or write to the cache which meant `no-cache` queries are silently incomplete when the `@client` field value was handled by a cache `read` function.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`5776ea0`](https://github.com/apollographql/apollo-client/commit/5776ea0db1f082663dcf470c3b22b9182a3eea28) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Update the `accept` header used with the `GraphQL17Alpha9Handler` to `multipart/mixed;incrementalSpec=v0.2` to ensure the newest incremental delivery format is requested.

- [#12927](https://github.com/apollographql/apollo-client/pull/12927) [`45ebb52`](https://github.com/apollographql/apollo-client/commit/45ebb52bcb84b81ce3a066204456c2e20f3d4c98) Thanks [@jerelmiller](https://github.com/jerelmiller)! - `DeepPartial<Array<TData>>` now returns `Array<DeepPartial<TData>>` instead of `Array<DeepPartial<TData | undefined>>`.

- [#13071](https://github.com/apollographql/apollo-client/pull/13071) [`99ffe9a`](https://github.com/apollographql/apollo-client/commit/99ffe9a8ede1683d902101c5371807a8442fcdcb) Thanks [@phryneas](https://github.com/phryneas)! - `prerenderStatic`: Expose return value of `renderFunction` to userland, fix `aborted` property.

  This enables usage of `resumeAndPrerender` with React 19.2.

- [#13026](https://github.com/apollographql/apollo-client/pull/13026) [`05eee67`](https://github.com/apollographql/apollo-client/commit/05eee67e91b480252923879987534e81d2866aba) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Reduce the number of observables created by `watchFragment` by reusing existing observables as much as possible. This should improve performance when watching the same item in the cache multiple times after a cache update occurs.

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Handle `@stream` payloads that send multiple items in the same chunk when using the `Defer20220824Handler`.

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Handle an edge case with the `Defer20220824Handler` where an error for a `@stream` item that bubbles to the `@stream` boundary (such as an item returning `null` for a non-null array item) would write items from future chunks to the wrong array index. In these cases, the `@stream` field is no longer processed and future updates to the field are ignored. This prevents runtime errors that TypeScript would otherwise not be able to catch.

- [#13081](https://github.com/apollographql/apollo-client/pull/13081) [`1e06ad7`](https://github.com/apollographql/apollo-client/commit/1e06ad7399716139fcfbec7423697eafc5750f5e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Avoid calling `merge` functions more than once for the same incremental chunk.

## 4.1.0-rc.1

### Patch Changes

- [#13086](https://github.com/apollographql/apollo-client/pull/13086) [`1a1d408`](https://github.com/apollographql/apollo-client/commit/1a1d4088f549088d4af3ff1f2d08d1c8e9af2a4d) Thanks [@phryneas](https://github.com/phryneas)! - Change the returned value from `null` to `{}` when all fields in a query were skipped.

  This also fixes a bug where `useSuspenseQuery` would suspend indefinitely when all fields were skipped.

- [#13071](https://github.com/apollographql/apollo-client/pull/13071) [`99ffe9a`](https://github.com/apollographql/apollo-client/commit/99ffe9a8ede1683d902101c5371807a8442fcdcb) Thanks [@phryneas](https://github.com/phryneas)! - `prerenderStatic`: Expose return value of `renderFunction` to userland, fix `aborted` property.

  This enables usage of `resumeAndPrerender` with React 19.2.

## 4.1.0-rc.0

### Minor Changes

- [#13078](https://github.com/apollographql/apollo-client/pull/13078) [`bf1e0dc`](https://github.com/apollographql/apollo-client/commit/bf1e0dcb2f6c9b94576dc6d049745f1869cd0043) Thanks [@phryneas](https://github.com/phryneas)! - Use the default stream merge function for `@stream` fields only if stream info is present. This change means that using the older `Defer20220824Handler` will not use the default stream merge function and will instead truncate the streamed array on the first chunk.

### Patch Changes

- [#13083](https://github.com/apollographql/apollo-client/pull/13083) [`f3c2be1`](https://github.com/apollographql/apollo-client/commit/f3c2be1665d8e2e260a4f55ec803d6e609748390) Thanks [@phryneas](https://github.com/phryneas)! - Expose the `ExtensionsWithStreamInfo` type for `extensions` in `Cache.writeQuery`, `Cache.write` and `Cache.update` so other cache implementations also can correctly access them.

- [#13082](https://github.com/apollographql/apollo-client/pull/13082) [`c257418`](https://github.com/apollographql/apollo-client/commit/c2574181f6b0d9ae059dfa3822a7842ec5f8ff1f) Thanks [@phryneas](https://github.com/phryneas)! - Pass `streamInfo` through result extensions as a `WeakRef`.

- [#13081](https://github.com/apollographql/apollo-client/pull/13081) [`1e06ad7`](https://github.com/apollographql/apollo-client/commit/1e06ad7399716139fcfbec7423697eafc5750f5e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Avoid calling `merge` functions more than once for the same incremental chunk.

## 4.0.12-beta.0

### Patch Changes

- [#12884](https://github.com/apollographql/apollo-client/pull/12884) [`d329790`](https://github.com/apollographql/apollo-client/commit/d32979070381f1897c90fb276e25a0c8375cc29a) Thanks [@phryneas](https://github.com/phryneas)! - Ensure that `PreloadedQueryRef` instances are unsubscribed when garbage collected

- [#13069](https://github.com/apollographql/apollo-client/pull/13069) [`9cad04a`](https://github.com/apollographql/apollo-client/commit/9cad04a4228a5059ea330ac9d284407a363fc10d) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Truncate @stream arrays only on last chunk by default

## 4.1.0-alpha.9

### Minor Changes

- [#13056](https://github.com/apollographql/apollo-client/pull/13056) [`b224efc`](https://github.com/apollographql/apollo-client/commit/b224efc25515370c68b514405762e68a443e4a4a) Thanks [@jerelmiller](https://github.com/jerelmiller)! - `InMemoryCache` no longer filters out explicitly returned `undefined` items from `read` functions for array fields. This now makes it possible to create `read` functions on array fields that return partial data and trigger a fetch for the full list.

- [#13058](https://github.com/apollographql/apollo-client/pull/13058) [`121a2cb`](https://github.com/apollographql/apollo-client/commit/121a2cb68820727186ecd74ce1041ef95284682e) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add an `extensions` option to `cache.write`, `cache.writeQuery`, and `client.writeQuery`. This makes `extensions` available in cache `merge` functions which can be accessed with the other merge function options.

  As a result of this change, any `extensions` returned in GraphQL operations are now available in `merge` in the cache writes for these operations.

### Patch Changes

- [#13053](https://github.com/apollographql/apollo-client/pull/13053) [`23ca0ba`](https://github.com/apollographql/apollo-client/commit/23ca0ba895473b397805e6bcc70e0fcf987547c5) Thanks [@phryneas](https://github.com/phryneas)! - Use memoized observable mapping when using `watchFragment`, `useFragment` or `useSuspenseFragment`.

## 4.1.0-alpha.10

### Patch Changes

- [#13053](https://github.com/apollographql/apollo-client/pull/13053) [`23ca0ba`](https://github.com/apollographql/apollo-client/commit/23ca0ba895473b397805e6bcc70e0fcf987547c5) Thanks [@phryneas](https://github.com/phryneas)! - Use memoized observable mapping when using `watchFragment`, `useFragment` or `useSuspenseFragment`.

## 4.1.0-alpha.9

### Minor Changes

- [#13056](https://github.com/apollographql/apollo-client/pull/13056) [`b224efc`](https://github.com/apollographql/apollo-client/commit/b224efc25515370c68b514405762e68a443e4a4a) Thanks [@jerelmiller](https://github.com/jerelmiller)! - `InMemoryCache` no longer filters out explicitly returned `undefined` items from `read` functions for array fields. This now makes it possible to create `read` functions on array fields that return partial data and trigger a fetch for the full list.

## 4.1.0-alpha.8

### Minor Changes

- [#13043](https://github.com/apollographql/apollo-client/pull/13043) [`65e66ca`](https://github.com/apollographql/apollo-client/commit/65e66cafb6828b63d14b64877bbad47af95f66e4) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Support `headers` transport for enhanced client awareness.

## 4.1.0-alpha.7

### Minor Changes

- [#13038](https://github.com/apollographql/apollo-client/pull/13038) [`109efe7`](https://github.com/apollographql/apollo-client/commit/109efe7e4380b579c6a577982bd9a6e8c6a53892) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add the `from` option to `readFragment`, `watchFragment`, and `updateFragment`.

## 4.1.0-alpha.6

### Patch Changes

- [#13026](https://github.com/apollographql/apollo-client/pull/13026) [`05eee67`](https://github.com/apollographql/apollo-client/commit/05eee67e91b480252923879987534e81d2866aba) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Reduce the number of observables created by `watchFragment` by reusing existing observables as much as possible. This should improve performance when watching the same item in the cache multiple times after a cache update occurs.

## 4.1.0-alpha.5

### Patch Changes

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where errors parsed from incremental chunks in `ErrorLink` might throw when using the `GraphQL17Alpha9Handler`.

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Handle `@stream` payloads that send multiple items in the same chunk when using the `Defer20220824Handler`.

- [#13010](https://github.com/apollographql/apollo-client/pull/13010) [`7627000`](https://github.com/apollographql/apollo-client/commit/76270002254b0c6acb18872a39ab180f9f1e4067) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Handle an edge case with the `Defer20220824Handler` where an error for a `@stream` item that bubbles to the `@stream` boundary (such as an item returning `null` for a non-null array item) would write items from future chunks to the wrong array index. In these cases, the `@stream` field is no longer processed and future updates to the field are ignored. This prevents runtime errors that TypeScript would otherwise not be able to catch.

## 4.1.0-alpha.4

### Patch Changes

- [#13009](https://github.com/apollographql/apollo-client/pull/13009) [`259ae9b`](https://github.com/apollographql/apollo-client/commit/259ae9bafaa8122996b0a52dd99828b2261087e5) Thanks [@phryneas](https://github.com/phryneas)! - Allow `FragmentType` not only to be called as `FragmentType<TData>`, but also as `FragmentType<TypedDocumentNode>`.

- [#13012](https://github.com/apollographql/apollo-client/pull/13012) [`44706a2`](https://github.com/apollographql/apollo-client/commit/44706a2e7ae2c977fa917214a1ff5e5fe4a9b3a7) Thanks [@phryneas](https://github.com/phryneas)! - Add helper type `QueryRef.ForQuery<TypedDocumentNode>`

## 4.1.0-alpha.3

### Minor Changes

- [#12971](https://github.com/apollographql/apollo-client/pull/12971) [`d11eb40`](https://github.com/apollographql/apollo-client/commit/d11eb40aa41d90ac664705bac01158d58bf55e9b) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for `from: null` in `client.watchFragment` and `cache.watchFragment`. When `from` is `null`, the emitted result is:

  ```ts
  {
    data: null,
    dataState: "complete",
    complete: true,
  }
  ```

- [#12971](https://github.com/apollographql/apollo-client/pull/12971) [`d11eb40`](https://github.com/apollographql/apollo-client/commit/d11eb40aa41d90ac664705bac01158d58bf55e9b) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for arrays with `useFragment`, `useSuspenseFragment`, and `client.watchFragment`. This allows the ability to use a fragment to watch multiple entities in the cache. Passing an array to `from` will return `data` as an array where each array index corresponds to the index in the `from` array.

  ```ts
  function MyComponent() {
    const result = useFragment({
      fragment,
      from: [item1, item2, item3],
    });

    // `data` is an array with 3 items
    console.log(result); // { data: [{...}, {...}, {...}], dataState: "complete", complete: true }
  }
  ```

- [#12971](https://github.com/apollographql/apollo-client/pull/12971) [`d11eb40`](https://github.com/apollographql/apollo-client/commit/d11eb40aa41d90ac664705bac01158d58bf55e9b) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add a `getCurrentResult` function to the observable returned by `client.watchFragment` and `cache.watchFragment` that returns the current value for the watched fragment.

  ```ts
  const observable = client.watchFragment({
    fragment,
    from: { __typename: "Item", id: 1 },
  });

  console.log(observable.getCurrentResult());
  // {
  //   data: {...},
  //   dataState: "complete",
  //   complete: true,
  // }
  ```

### Patch Changes

- [#12971](https://github.com/apollographql/apollo-client/pull/12971) [`d11eb40`](https://github.com/apollographql/apollo-client/commit/d11eb40aa41d90ac664705bac01158d58bf55e9b) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Deduplicate watches created by `useFragment`, `client.watchFragment`, and `cache.watchFragment` that contain the same fragment, variables, and identifier. This should improve performance in situations where a `useFragment` or a `client.watchFragment` is used to watch the same object in multiple places of an application.

- [#12982](https://github.com/apollographql/apollo-client/pull/12982) [`5c56b32`](https://github.com/apollographql/apollo-client/commit/5c56b3210a2c03e247ec9e600f1e27eb71df5e96) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ignore top-level `data` values on subsequent chunks in incremental responses.

- [#12982](https://github.com/apollographql/apollo-client/pull/12982) [`5c56b32`](https://github.com/apollographql/apollo-client/commit/5c56b3210a2c03e247ec9e600f1e27eb71df5e96) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix the `Defer20220824Handler.SubsequentResult` type to match the `FormattedSubsequentIncrementalExecutionResult` type in `graphql@17.0.0-alpha.2`.

- [#12973](https://github.com/apollographql/apollo-client/pull/12973) [`072da24`](https://github.com/apollographql/apollo-client/commit/072da24a8daec3a646ef0cce30de32f95ea0bb23) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Update the `accept` header used with the `GraphQL17Alpha9Handler` to `multipart/mixed;incrementalSpec=v0.2` to ensure the newest incremental delivery format is requested.

- [#12971](https://github.com/apollographql/apollo-client/pull/12971) [`d11eb40`](https://github.com/apollographql/apollo-client/commit/d11eb40aa41d90ac664705bac01158d58bf55e9b) Thanks [@jerelmiller](https://github.com/jerelmiller)! - `DeepPartial<Array<TData>>` now returns `Array<DeepPartial<TData>>` instead of `Array<DeepPartial<TData | undefined>>`.

## 4.1.0-alpha.2

### Minor Changes

- [#12959](https://github.com/apollographql/apollo-client/pull/12959) [`556e837`](https://github.com/apollographql/apollo-client/commit/556e83781069d925a7e8f99e49023f6f858c6438) Thanks [@jerelmiller](https://github.com/jerelmiller)! - You can now provide a callback function as the `context` option on the `mutate` function returned by `useMutation`. The callback function is called with the value of the `context` option provided to the `useMutation` hook. This is useful if you'd like to merge the context object provided to the `useMutation` hook with a value provided to the `mutate` function.

  ```ts
  function MyComponent() {
    const [mutate, result] = useMutation(MUTATION, {
      context: { foo: true },
    });

    async function runMutation() {
      await mutate({
        // sends context as { foo: true, bar: true }
        context: (hookContext) => ({ ...hookContext, bar: true }),
      });
    }

    // ...
  }
  ```

### Patch Changes

- [#12954](https://github.com/apollographql/apollo-client/pull/12954) [`1c82eaf`](https://github.com/apollographql/apollo-client/commit/1c82eafe4921a9e30128202623be6c5a3d4df803) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure an error is thrown when `@stream` is detected and an `incrementalDelivery` handler is not configured.

## 4.1.0-alpha.1

### Minor Changes

- [#12934](https://github.com/apollographql/apollo-client/pull/12934) [`54ab6d9`](https://github.com/apollographql/apollo-client/commit/54ab6d994692dad9f06d3d0b84c84d021d126577) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Don't set the fallback value of a `@client` field to `null` when a `read` function is defined. Instead the `read` function will be called with an `existing` value of `undefined` to allow default arguments to be used to set the returned value.

  When a `read` function is not defined nor is there a defined resolver for the field, warn and set the value to `null` only in that instance.

- [#12934](https://github.com/apollographql/apollo-client/pull/12934) [`54ab6d9`](https://github.com/apollographql/apollo-client/commit/54ab6d994692dad9f06d3d0b84c84d021d126577) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add an abstract `resolvesClientField` function to `ApolloCache` that can be used by caches to tell `LocalState` if it can resolve a `@client` field when a local resolver is not defined.

  `LocalState` will emit a warning and set a fallback value of `null` when no local resolver is defined and `resolvesClientField` returns `false`, or isn't defined. Returning `true` from `resolvesClientField` signals that a mechanism in the cache will set the field value. In this case, `LocalState` won't set the field value.

### Patch Changes

- [#12915](https://github.com/apollographql/apollo-client/pull/12915) [`c97b145`](https://github.com/apollographql/apollo-client/commit/c97b145188d39d754ff098ff399a80cae5b10cc0) Thanks [@phryneas](https://github.com/phryneas)! - Create mechanism to add experimental features to Apollo Client

- [#12934](https://github.com/apollographql/apollo-client/pull/12934) [`54ab6d9`](https://github.com/apollographql/apollo-client/commit/54ab6d994692dad9f06d3d0b84c84d021d126577) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure `LocalState` doesn't try to read from the cache when using a `no-cache` fetch policy.

- [#12934](https://github.com/apollographql/apollo-client/pull/12934) [`54ab6d9`](https://github.com/apollographql/apollo-client/commit/54ab6d994692dad9f06d3d0b84c84d021d126577) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Warn when using a `no-cache` fetch policy without a local resolver defined. `no-cache` queries do not read or write to the cache which meant `no-cache` queries are silently incomplete when the `@client` field value was handled by a cache `read` function.

## 4.1.0-alpha.0

### Minor Changes

- [#12923](https://github.com/apollographql/apollo-client/pull/12923) [`2aa31c7`](https://github.com/apollographql/apollo-client/commit/2aa31c718155e88814551afb14fd7a0035acc57d) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where deferred payloads that reteurned arrays with fewer items than the original cached array would retain items from the cached array. This change includes `@stream` arrays where stream arrays replace the cached arrays.

- [#12926](https://github.com/apollographql/apollo-client/pull/12926) [`c7fba99`](https://github.com/apollographql/apollo-client/commit/c7fba99e16da522fdbc35b9c16cdb8df0dda4c2c) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Support the newer incremental delivery format for the `@defer` directive implemented in `graphql@17.0.0-alpha.9`. Import the `GraphQL17Alpha9Handler` to use the newer incremental delivery format with `@defer`.

  ```ts
  import { GraphQL17Alpha9Handler } from "@apollo/client/incremental";

  const client = new ApolloClient({
    // ...
    incrementalHandler: new GraphQL17Alpha9Handler(),
  });
  ```

  > [!NOTE]
  > In order to use the `GraphQL17Alpha9Handler`, the GraphQL server MUST implement the newer incremental delivery format. You may see errors or unusual behavior if you use the wrong handler. If you are using Apollo Router, continue to use the `Defer20220824Handler` because Apollo Router does not yet support the newer incremental delivery format.

- [#12918](https://github.com/apollographql/apollo-client/pull/12918) [`562e219`](https://github.com/apollographql/apollo-client/commit/562e2191a4b38e05edb3da9074e2958db3c7b6b9) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Add support for the `@stream` directive on both the `Defer20220824Handler` and the `GraphQL17Alpha2Handler`.

  > [!NOTE]
  > The implementations of `@stream` differ in the delivery of incremental results between the different GraphQL spec versions. If you upgrading from the older format to the newer format, expect the timing of some incremental results to change.

### Patch Changes

- [#12925](https://github.com/apollographql/apollo-client/pull/12925) [`f538a83`](https://github.com/apollographql/apollo-client/commit/f538a83621e1d110286c056dd8e91611dfd9a1d3) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where calling `fetchMore` with `@defer` or `@stream` would not rerender incremental results as they were streamed.

- [#12923](https://github.com/apollographql/apollo-client/pull/12923) [`01cace0`](https://github.com/apollographql/apollo-client/commit/01cace0a6d4faf79e8a4188b93c7d13c4b26d6d4) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Improve the cache data loss warning message when `existing` or `incoming` is an array.

## 4.0.13

### Patch Changes

- [#13094](https://github.com/apollographql/apollo-client/pull/13094) [`9cbe2c2`](https://github.com/apollographql/apollo-client/commit/9cbe2c2dd2282ac861327d3c394578db7706df05) Thanks [@phryneas](https://github.com/phryneas)! - Ensure that `compact` and `mergeOptions` preserve symbol keys.

  This fixes an issue where the change introduced in 4.0.11 via #13049 would not
  be applied if `defaultOptions` for `watchQuery` were declared.

  Please note that `compact` and `mergeOptions` are considered internal utilities
  and they might have similar behavior changes in future releases.
  Do not use them in your application code - a change like this is not considered
  breaking and will not be announced as such.

## 4.0.12

### Patch Changes

- [#13077](https://github.com/apollographql/apollo-client/pull/13077) [`f322460`](https://github.com/apollographql/apollo-client/commit/f322460fe9baae82c0980dd082c1b6b4956a4951) Thanks [@phryneas](https://github.com/phryneas)! - Fix a potential memory leak where Trie nodes would remain in memory too long.

## 4.0.11

### Patch Changes

- [#13050](https://github.com/apollographql/apollo-client/pull/13050) [`8020829`](https://github.com/apollographql/apollo-client/commit/8020829d8a3bdb3219a37e8d1f7b89179f721037) Thanks [@phryneas](https://github.com/phryneas)! - Replace usage of `findLast` with more backwards-compatible methods.

- [#13049](https://github.com/apollographql/apollo-client/pull/13049) [`05638de`](https://github.com/apollographql/apollo-client/commit/05638deaf598c5bf5d03b82d7deaf57468546229) Thanks [@phryneas](https://github.com/phryneas)! - Fixes an issue where queries starting with `skipToken` or lazy queries from `useLazyQuery` were included in `client.refetchQueries()` before they had been executed for the first time. While generally queries with a `standby` `fetchPolicy` should be included in refetch, these queries never had `variables` passed in, so they should be excluded until they have run once and received their actual variables.

  These queries are now properly excluded from refetch operations until after their initial execution.

  This change adds a new hidden option to `client.watchQuery`, `[variablesUnknownSymbol]`, which may be set `true` for queries starting with a `fetchPolicy` of `standby`. It will only be applied when creating the `ObservableQuery` instance and cannot be changed later. This flag indicates that the query's variables are not yet known, and thus it should be excluded from refetch operations until they are.
  **This option is not meant for everyday use and is intended for framework integrations only.**

## 4.0.10

### Patch Changes

- [#13045](https://github.com/apollographql/apollo-client/pull/13045) [`af4acdc`](https://github.com/apollographql/apollo-client/commit/af4acdc88bd3bac0d697ab300816241e4065842c) Thanks [@phryneas](https://github.com/phryneas)! - Fix memory leak #13036

## 4.0.9

### Patch Changes

- [#12993](https://github.com/apollographql/apollo-client/pull/12993) [`8f3bc9b`](https://github.com/apollographql/apollo-client/commit/8f3bc9b7253a737062dc0d652cd4f8b354f68ccc) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Fix an issue where switching from options with `variables` to `skipToken` with `useSuspenseQuery` and `useBackgroundQuery` would create a new `ObservableQuery`. This could cause unintended refetches where `variables` were absent in the request when the query was referenced with `refetchQueries`.

## 4.0.8

### Patch Changes

- [#12983](https://github.com/apollographql/apollo-client/pull/12983) [`f6d0efa`](https://github.com/apollographql/apollo-client/commit/f6d0efac4d99375c67255aee6d9b2981753b6f55) Thanks [@CarsonF](https://github.com/CarsonF)! - Fix cache.modify() mapping readonly arrays to singular reference

## 4.0.7

### Patch Changes

- [#12950](https://github.com/apollographql/apollo-client/pull/12950) [`5b4f36a`](https://github.com/apollographql/apollo-client/commit/5b4f36a2b249d15e2e8165bd32d9b2fca7e70217) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Don't send `operationType` in the payload sent by `GraphQLWsLink`.

## 4.0.6

### Patch Changes

- [#12937](https://github.com/apollographql/apollo-client/pull/12937) [`3b0d89b`](https://github.com/apollographql/apollo-client/commit/3b0d89bc9dde3eaee9ddf0aec387da43fe71abc0) Thanks [@phryneas](https://github.com/phryneas)! - Fix a problem with `fetchMore` where the loading state wouldn't reset if the result wouldn't result in a data update.

## 4.0.5

### Patch Changes

- [#12920](https://github.com/apollographql/apollo-client/pull/12920) [`e2fc385`](https://github.com/apollographql/apollo-client/commit/e2fc3850ddb2aa756fc44420390ae357daf31948) Thanks [@phryneas](https://github.com/phryneas)! - Fix an invariance type error in the `MockedResponse` type.

## 4.0.4

### Patch Changes

- [#12892](https://github.com/apollographql/apollo-client/pull/12892) [`db8a04b`](https://github.com/apollographql/apollo-client/commit/db8a04b193c157d57d6fe0f187b1892afdda1b7d) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Prevent unhandled rejections from the promise returned by calling the `mutate` function from the `useMutation` hook.

- [#12899](https://github.com/apollographql/apollo-client/pull/12899) [`5352c12`](https://github.com/apollographql/apollo-client/commit/5352c1208e19c93678fef7860a1a87841653eb64) Thanks [@phryneas](https://github.com/phryneas)! - Fix an issue when `invariant` is called by external libraries when no dev error message handler is loaded.

- [#12895](https://github.com/apollographql/apollo-client/pull/12895) [`71f2517`](https://github.com/apollographql/apollo-client/commit/71f2517132a34563a14934f3971666b3691710f9) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Support `skipToken` with `useQuery` to provide a more type-safe way to skip query execution.

  ```ts
  import { skipToken, useQuery } from "@apollo/client/react";

  // Use `skipToken` in place of `skip: true` for better type safety
  // for required variables
  const { data } = useQuery(QUERY, id ? { variables: { id } } : skipToken);
  ```

  Note: this change is provided as a patch within the 4.0 minor version because the changes to TypeScript validation with required variables in version 4.0 made using the `skip` option more difficult.

- [#12900](https://github.com/apollographql/apollo-client/pull/12900) [`c0d5be7`](https://github.com/apollographql/apollo-client/commit/c0d5be7cbbb1b1f7771962eb2ae0e173de743265) Thanks [@phryneas](https://github.com/phryneas)! - Use named export `equal` instead of default from `"@wry/equality"`

## 4.0.3

### Patch Changes

- [#12887](https://github.com/apollographql/apollo-client/pull/12887) [`6f6ca47`](https://github.com/apollographql/apollo-client/commit/6f6ca47e9f5e80ee9c98fca2639b5cba6317fbbf) Thanks [@phryneas](https://github.com/phryneas)! - Fix accidental deep re-export from `/react` out of `/react/internals`

- [#12890](https://github.com/apollographql/apollo-client/pull/12890) [`019b422`](https://github.com/apollographql/apollo-client/commit/019b4224147a5a8709de54c4474e126619dd2469) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Ensure the `variables` option for `useMutation` provides proper IntelliSense suggestions.

## 4.0.2

### Patch Changes

- [#12880](https://github.com/apollographql/apollo-client/pull/12880) [`56fac52`](https://github.com/apollographql/apollo-client/commit/56fac522549eaed5494097dc0098ea7a558382a0) Thanks [@phryneas](https://github.com/phryneas)! - restore `getMemoryInternals` access in dev builds

## 4.0.1

### Patch Changes

- [#12876](https://github.com/apollographql/apollo-client/pull/12876) [`b00f231`](https://github.com/apollographql/apollo-client/commit/b00f231e5f10a23178cf7a2c69a4e13cd959ab45) Thanks [@phryneas](https://github.com/phryneas)! - Fix CJS build output for `invariantErrorCodes`

- [#12866](https://github.com/apollographql/apollo-client/pull/12866) [`0d1614a`](https://github.com/apollographql/apollo-client/commit/0d1614a9dfca2b1bcf4ea40095cc9018d6314532) Thanks [@jerelmiller](https://github.com/jerelmiller)! - Export `isNetworkStatusInFlight` from `@apollo/client/utilities`. Add `isNetworkStatusSettled` to `@apollo/client/utilities` and re-export it from `@apollo/client` with a deprecation.

## 4.0.0

# Apollo Client 4.0 Release Notes

Apollo Client 4.0 delivers a more modern, efficient, and type-safe GraphQL client experience through various architectural improvements and API refinements. This release focuses on developer experience, bundle size optimization, and framework flexibility.

## Key Improvements

### 🎯 Framework-Agnostic Core

Apollo Client 4.0 separates React functionality from the core library, making `@apollo/client` truly framework-agnostic. React exports now live in `@apollo/client/react`, allowing developers to use Apollo Client with any JavaScript framework without React dependencies.

### 📦 Smaller Bundle Sizes

- **Opt-in Local State Management**: The `@client` directive functionality is now opt-in via the `LocalState` class, reducing bundle size when not using local state
- **Modern Build Target**: Transpiled to target `since 2023, node >= 20, not dead`, leveraging modern JavaScript features for better performance
- **Improved Tree-Shaking**: Proper `exports` field in package.json enables better dead code elimination

### 💥 Unified Error Handling

Apollo Client 4.0 completely reimagines error handling for better clarity and debugging:

- `ApolloError` removed in favor of specific error classes
- Unification of errors to a single `error` property
- Network errors now respect `errorPolicy` settings
- External errors passed through without wrapping
- New, more granular error classes with static `.is()` methods for robust type narrowing

### 🔧 Enhanced TypeScript Support

- **Namespaced Types**: Types are now colocated with their APIs (e.g., `useQuery.Options` instead of `QueryHookOptions`)
- **Precise Return Types**: Return types accurately reflect the options passed (e.g., `returnPartialData` makes `data` type `DeepPartial<TData>`)
- **Stricter Type Safety**: Required variables are now enforced more consistently throughout the client
- **New `dataState` Property**: Enables accurate type narrowing of query results
- **Module Augmentation**: Custom context types via declaration merging instead of fragile generics
- **Cust