reqsrv

Typed SDK factory for web APIs

• Type-safe request handler based on a custom API schema
• Shared interface for handling API requests on the client and the server
• No internal dependence on a specific request utility

Installation: npm i reqsrv

RequestService

The RequestService class helps create a type-safe entrypoint to an API:

import {RequestService} from 'reqsrv';

let service = new RequestService<APISchema>(fetchData);

The constructor accepts a custom request handler fetchData. A specific request handler isn't built into the package, since it can vary in many ways depending on the purpose and environment of the application (it might make use of fetch, node-fetch, axios, logging, default headers, or whatever necessary).

The purpose of RequestService is to offer a consistent environment-agnostic interface to request handling on top of a typed API schema.

🔹 A typed schema allows to prevalidate request inputs at compile-time and highlight mismatches in a type-aware IDE.

🔹 The environment-agnostic interface works consistently throughout the client and the server:

let browserClient = new RequestService<APISchema>(clientHandler);

let serverClient = new RequestService<APISchema>(serverHandler);

Same API schema, same request interface, same reusable related code, different environment-specific request handlers.

Schema definition

The APISchema type used with the RequestService constructor is a custom schema outlining the types of requests and responses within an API. The example below shows what such a schema may look like.

import type {Schema} from 'reqsrv';

// wrapping into the `Schema` generic type is optional, but
// this helps validate the basic schema structure
export type APISchema = Schema<{
    // a schema key can be any unique string, for an HTTP API
    // a pair of a method and a path can serve this purpose
    'GET /items/:id': {
        request: {
            // `params` can be omitted if the URL path is fixed and
            // has no parameter placeholders
            params: {
                id: number;
            };
            query?: {
                mode?: 'compact' | 'full';
            };
        };
        response: {
            body: {
                id: number;
                name?: string;
            };
        };
    };
    'POST /items/:id': {
        // ...
    };
    'GET /items': {
        // ...
    };
    // ... and so forth
}>;

With such a schema assigned to service, calls to its send() method will be prevalidated against this schema, which means that a type-aware IDE will warn of type mismatches or typos in the parameters:

let {ok, status, body} = await service.send('GET /items/:id', {
    params: {
        id: 10,
    },
    query: {
        mode: 'full',
    },
});

The options passed as the second parameter to send() are validated as APISchema['GET /items/:id'] based on the schema type passed to the RequestService constructor and the first parameter passed to send().

Shorthand methods

The API schema keys can be mapped to custom method names:

let api = service.getEntry({
    getItems: 'GET /items',
    getItem: 'GET /items/:id',
    setItem: 'POST /items/:id',
});

With such a mapping in place, service.send('GET /items/:id', {...}) has another equivalent form:

let response = await api.getItem({
    params: {
        id: 10,
    },
    query: {
        mode: 'full',
    },
});

The getEntry() method doesn't have to take all the API schema keys at once. The API methods can be split into logical scopes:

let api = {
    users: service.getEntry({
        getList: 'GET /users',
        getInfo: 'GET /users/:id',
    }),
    items: service.getEntry({
        getList: 'GET /items',
        getInfo: 'GET /items/:id',
        setInfo: 'POST /items/:id',
    }),
};

let userList = await api.users.getList();
let firstUser = await api.users.getInfo({params: {id: userList[0].id}});

For API methods controlled only with query parameters, there is also a shorthand option: the getQueryEntry() method, returning aliases accepting only query parameters, without the need to nest them into the query key.

Custom request handler

As shown above, the RequestService constructor takes a custom request handler as a parameter. Internal independence of RequestService from a fixed built-in request handler allows to handle requests of all sorts and environments (the browser or node) without locking in with a certain approach to handling requests.

Here's an example of a basic JSON request handler that can be passed to RequestService:

import {
    RequestHandler,
    RequestError,
    getRequestAction,
    toStringValueMap,
} from 'reqsrv';

const endpoint = 'https://api.example.com';

export const fetchJSON: RequestHandler = async (target, request) => {
    let {method, url} = getRequestAction({request, target, endpoint});

    let response = await fetch(url, {
        method,
        headers: toStringValueMap(request?.headers),
        body: request?.body ? JSON.stringify(request?.body) : null,
    });

    let {ok, status, statusText} = response;

    if (!ok) {
        throw new RequestError({
            status,
            statusText,
        });
    }

    try {
        return {
            ok,
            status,
            statusText,
            body: await response.json(),
        };
    }
    catch (error) {
        throw new RequestError(error);
    }
}

To meet the needs of a specific use case, the request handler's code can certainly depart from the example above (which is again the reason why it's not hardwired into the package).