@savvagent/kestrel

kestrel

kestrel is an isomorphic class-based means of extending fetch, either window.fetch or global.fetch in NodeJS.

kestrel enhances fetch with interceptors without polluting fetch itself. It does so by embracing a class-based approach. Interceptors consist of objects that include one or more functions which are processed in order. Functions that can be included in interceptor objects include request, requestError, response and/or responseError. Interceptors are simple to write and share. This repo includes standard interceptors for making JSON requests, handling response errors and receiving JSON responses.

Benefits of Approach

kestrel has the following benefits over plain fetch and other approaches to wrap fetch:

• tiny - it is 2.2KB unminified.
• it has method shortcuts, such as fc.get(), fc.post(), etc.
• it automatically dedupes requests and caches responses
• global fetch, whether window.fetch or node-fetch remains untouched. It is not monkey patched.
• class based - You can create more than one instance if necessary to accommodate different APIs. Naturally, instances are isolated.
• interceptors can be swapped on the fly.
• interceptors can be overloaded.
• interceptors can be shared.
• you can build complex solutions.

Dependencies

Global fetch is required. kestrel has been tested against window.fetch, node-fetch and isomorphic-fetch. NodeJS 6x or greater is required.

kestrel has been developed with modern Javascript. Your project must be able to consume EcmaScript modules or CommonJS in node.

Installation

kestrel can be installed with either npm or yarn.

yarn add @savvagent-os/kestrel

or

npm i @savvagent-os/kestrel -S

Use

Here are some ways of using kestrel.

You can use some interceptors included with kestrel.

import { Kestrel, jsonRequest, jsonResponse } from '@savvagent-os/kestrel';
const interceptors = [jsonRequest, jsonResponse];
const client = new Kestrel(interceptors);

const resp = await client.request('http://some.url/', fetchOptions = {});

You can create your own interceptors and add and remove them dynamically.

import { Kestrel } from '@savvagent-os/kestrel';
import { interceptor, interceptor1, interceptor2 } from '../interceptors';

const client = new Kestrel();

client register(interceptor);

//register interceptor1 ahead of interceptor
client.register(interceptor1, 0);

// register interceptor2 at the end of the interceptor chain
client.register(interceptor2)

// get the current interceptors
const interceptors = client.getInterceptors();

// remove an interceptor
client.unregister(interceptorId)

// remove all the interceptors - useful for testing
client.clear();

// make requests
const url = 'https://gitlab.com/projects';

client.get(url)
  .then(response => console.log('response', response))
  .catch(error => console.log('error', error))

API

Kestrel

fc.clear() fc.delete(url, options) fc.get(url, options) fc.head(url, options) fc.patch(url, options) fc.post(url, options) fc.put(url, options) fc.register(interceptor or array of interceptors) fc.request(url, options) fc.unregister(interceptorId)

Interceptors

Interceptors are objects that must have at least one of the following functions: request, requestError, response, responseError. Hopefully, the purpose of the functions is clear from the names.

Interceptors run in order. So if I had an interceptor designed to catch network errors, I would want that interceptor to the first interceptor in the interceptor chain.

Interceptor Internals

An interceptor is an object that has a unique id and includes one or more permitted functions.

export default {
  request(url, config = {}) {
    Object.assign(config, {headers: {Accept: 'application/json'}});
    return [url, config];
  },
  requestError(error) {
    return Promise.reject(error);
  },
  response(response) {
    // modify the response
    return response;
  },
  responseError(error) {
    return Promise.reject(error);
  }
  id: 'JSON_REQUEST'
};

You can create interceptors for various needs. For example, here's an audio interceptor:

export const audioInterceptor = {
  const source = audioCtx.createBufferSource();
  response(response) {
    return response.arrayBuffer()
      .then(buffer => audioCtx.decodeAudioData(buffer, decodedData => {
        source.buffer = decodedData;
        source.connect(audioCtx.destination);
      }))
      .then(() => source);
  }
  id: 'AUDIO_INTERCEPTOR'
}

Interceptor methods (request, requestError, response, responseError) can incorporate promises.

const url = 'http://dummy.restapiexample.com/api/v1/employees';
const p = Promise.resolve({session: '124-64-74-311157-537524-7453-8889-19-11886119-5-2512148-7874-6612768-86-9052812935'});

const interceptor = {
  async request(url = "", config = {}) {
    const prom = await p;
    const u = `${url}?session=${prom.session}`
    return [u, config];
  },
  id: 'PROMISE_REQUEST'
}

const client = new Kestrel([interceptor]);
const response = await client.request(url);
console.log(response.url.includes(session)) // true

const url = 'http://dummy.restapiexample.com/api/v1/employees';
const p = Promise.resolve({thingy: 'foo'});

const interceptor = {
  async response(response) {
    if (response.status === 204 || response.status === 201) return {};
    const text = await response.text();
    const json = JSON.parse(text);
    const { data } = json;
    const resolvedPromise = await p;
    const arr = data.map(datum => ({
      ...datum,
      ...resolvedPromise
    }))
    return arr;
  },
  id: 'PROMISE_RESPONSE'
}
client = new Kestrel([interceptor]);
const response = await client.request(url);
response.forEach(item => expect(item.thingy).to.equal('foo'))