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State: Context Objects

The $.context object is how routes share in-memory state. It's an instance of the Context class exported from _.context.ts in the same directory (or the nearest parent directory that has one).

// routes/pet.ts
export const POST: HTTP_POST = ($) => {
  return $.response[200].json($.context.addPet($.body));
};

// routes/pet/{petId}.ts
export const GET: HTTP_GET = ($) => {
  const pet = $.context.getPetById($.path.petId);
  if (pet === undefined)
    return $.response[404].text(`Pet ${$.path.petId} not found.`);
  return $.response[200].json(pet);
};

Customize _.context.ts to hold whatever state and business logic your mock needs:

// routes/_.context.ts
export class Context {
  pets: Pet[] = [];

  addPet(pet: Pet) {
    const id = this.pets.length;
    this.pets.push({ ...pet, id });
    return this.pets[id];
  }

  getPetById(id: number) {
    return this.pets[id];
  }
}

Important

Keep context in memory. Counterfact is a development tool — starting fresh each time is a feature, not a bug. In-memory state also makes the server very fast.

Nested contexts

For large APIs you can nest context objects. Any subdirectory can have its own _.context.ts. One context can access another via the loadContext function passed to its constructor:

// routes/users/_.context.ts
export class Context {
  constructor({ loadContext }) {
    this.rootContext = loadContext("/");
    this.petsContext = loadContext("/pets");
  }
}

Loading JSON data with readJson

Use the readJson function (also passed to the constructor) to load static JSON data into your context. The path is resolved relative to the _.context.ts file.

// routes/_.context.ts
export class Context {
  private readonly readJson: (path: string) => Promise<unknown>;

  constructor({ readJson }: { readJson: (path: string) => Promise<unknown> }) {
    this.readJson = readJson;
  }

  async getSeeds() {
    return this.readJson("../mocks/seeds.json");
  }
}

See also