API Server

Type-safe API server with JSON schema validation.

const schema = {
	response: {
		200: {
			type: "object",
			properties: {
				id: { type: "string" },
				name: { type: "string" },
				position: { type: "number" },
			},
			required: ["id", "name"],
			additionalProperties: false,
		},
		404: {
			type: "object",
			properties: {
				error: { type: "string" },
			},
			required: ["error"],
			additionalProperties: false,
		},
	},
	querystring: {
		type: "object",
		properties: {
			id: { type: "string" },
		},
		required: ["id"],
		additionalProperties: false,
	},
} as const satisfies BaseSchema

// this is the part that is shared between the client and the server
export const tracksRoute = define<typeof schema>({
	url: "/api/tracks",
	method: "get",
})

export const handler = procedure(schema, tracksRoute, {
	handler(request, reply) {
		const { id } = request.query
		const track = tracks.find((track) => track.id === id)
		if (track) {
			reply.code(200).send(track)
		} else {
			reply.code(404).send({ error: "Track not found" })
		}
	},
})

With Fastify, using a JSON schema to validate the inputs and outputs makes the requests have 10-20% more throughput ¹. And using our own define and procedure functions we can use the same schema to provide type safety on the client side and on the server side.

Under the hood, fastify uses Ajv to validate the schema at runtime, and we use json-schema-to-ts to obtain TypeScript types from the schemas.

API Server

See also

Client API

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