MappedFactory

Creates output values by mapping a completed input object.

Use this factory when the values you want to override are easiest to model as an object, but the final value should be a different shape or type. Each call to make builds the input defaults, applies deep partial overrides, and passes the completed input to the mapper function.

The mapper function can also declare dependencies, which are passed to make after the overrides, in the same way as AsyncMappedFactory. Use them for the things the mapper needs that are not part of the input, such as a client or a piece of configuration. They are given at call time rather than held by the factory, and are used as they are given, never fetched or awaited.

Usage

interface UrlParts {
  protocol: "https";
  host: string;
  path: string;
}

const urlFactory = new MappedFactory<UrlParts, string>(
  () => ({
    protocol: "https",
    host: "example.com",
    path: "/users",
  }),
  (parts) => `${parts.protocol}://${parts.host}${parts.path}`,
);

const defaultUrl = urlFactory.make();
// "https://example.com/users"

const apiUrl = urlFactory.make({ path: "/api/users" });
// "https://example.com/api/users"

// The same factory with the host supplied as a dependency:
const hostedUrlFactory = new MappedFactory<
  Omit<UrlParts, "host">,
  string,
  { server: { host: string } }
>(
  () => ({
    protocol: "https",
    path: "/users",
  }),
  (parts, { server }) => `${parts.protocol}://${server.host}${parts.path}`,
);

const hostedUrl = hostedUrlFactory.make({ path: "/api/users" }, { server });
// "https://test.example.com/api/users"

Source

Source file: src/mapped/mapped-factory.ts