Minor Changes

• #13274 7b10078 Thanks @jerelmiller! - Adds Scalar.fromGraphQLScalarType helper to create a Scalar instance from an existing graphql.js GraphQLScalarType.

  import { GraphQLScalarType } from "graphql";
  import { Scalar } from "@apollo/client";
  
  const dateTimeScalarType = new GraphQLScalarType<Date, string>({
    // ...
  });
  
  const dateTimeScalar = Scalar.fromGraphQLScalarType(dateTimeScalarType, {
    is: (value) => value instanceof Date,
  });
  

• #13252 ed86234 Thanks @jerelmiller! - Adds the plumbing and types implementation for declaring custom scalars and configuring custom scalars in InMemoryCache.

  You can declare custom scalar types with declaration merging on the ApolloCache.Scalars interface:

  // apollo.d.ts
  import "@apollo/client";
  
  declare module "@apollo/client" {
    namespace ApolloCache {
      interface Scalars {
        Date: { serialized: string; parsed: Date };
      }
    }
  }
  

  This enables the scalars option in InMemoryCache:

  import { Scalar } from "@apollo/client";
  
  const cache = new InMemoryCache({
    scalars: {
      Date: new Scalar({
        parse: (dateString) => new Date(dateString),
        serialize: (date) => date.toISOString(),
        is: (value) => value instanceof Date,
      }),
    },
  });
  

• #13259 ccaf686 Thanks @jerelmiller! - Adds a scalar option to InMemoryCache field policies that tells the cache which scalar to use when parsing or serializing the field value.

  import { Scalar } from "@apollo/client";
  
  new InMemoryCache({
    scalars: {
      DateTime: new Scalar({
        parse: (dateString) => new Date(dateString),
        serialize: (date) => date.toISOString(),
      }),
    },
    typePolicies: {
      Event: {
        fields: {
          startTime: {
            // Parse this field using the DateTime scalar
            scalar: "DateTime",
          },
        },
      },
    },
  });
  

  This scalar definition is now used to properly parse or serialize the field value for cache reads and writes as well as cache.extract() and cache.restore().

• #13273 0886de1 Thanks @jerelmiller! - Automatically serialize variables that include custom scalar values. This includes cache reads and writes as well as requests to the network.

  For more complex input objects, a new inputObjects option is available to InMemoryCache that specifies where nested scalar fields are found.

  const cache = new InMemoryCache({
    scalars: {
      DateTime: new Scalar({
        parse: (value) => new Date(value),
        serialize: (value) => value.toISOString(),
        is: (value) => value instanceof Date,
      }),
    },
    inputObjects: {
      EventFilter: {
        fields: {
          date: "DateTime",
        },
      },
    },
  });
  
  const client = new ApolloClient({ cache, link });
  
  await client.query({
    query: gql`
      query Event($filter: EventFilter!) {
        event(filter: $filter) {
          name
        }
      }
    `,
    variables: {
      filter: {
        date: new Date("2026-01-01T00:00:00.000Z"),
      },
    },
  });
  
  // The link receives:
  // { filter: { date: "2026-01-01T00:00:00.000Z" } }
  

• #13252 ed86234 Thanks @jerelmiller! - Adds the getScalar abstract method to ApolloCache that cache subclasses override to provide scalar behavior to Apollo Client. Defaults to unconditionally return undefined if not specified.