reqsrv

Utilities for typing web APIs

Features

• type-safe request handlers based on a custom API schema;
• common environment-agnostic interface for handling API requests;
• no internal dependence on a specific request utility.

Usage

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

import {RequestService} from 'reqsrv';

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

The constructor accepts a custom request handler fetchData. It's not predefined by 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 CustomSchema type used with the constructor is a custom schema outlining the types of requests and responses within an API, see the example below of 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 CustomSchema = 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 CustomSchema['GET /items/:id'] (based on the schema type passed to the RequestService constructor and the first parameter passed to send()).

Assigning custom method names to API targets

Schema keys can be mapped to new methods:

let api = service.assign({
    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 assign() method doesn't have to take all the API schema keys at once. The API methods can be split into logical subsets and arranged in different namespaces:

let api = {
    users: service.assign({
        getList: 'GET /users',
        getInfo: 'GET /users/:id',
    }),
    items: service.assign({
        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 assignQuery() 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 request library.

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).