Thwack. A tiny modern data fetching solution

TL;DR

Thwack is:

• 💻 Modern — Thwack is an HTTP data fetching solution built for modern browsers
• 🔎 Small — Thwack is only ~1.5k gzipped
• 👩‍🏫 Smarter — Built with modern JavaScript
• 😘 Familiar — Thwack uses an Axios-like interface
• 🅰️ Typed — Easier inclusion for TypeScript projects
• ✨ Support for NodeJS 10 and 12

This README is a work in progress. You can also ask me a question on Twitter.

Installation

$ npm i thwack

or

$ yarn add thwack

Why Thwack over Axios?

Axios was great when it was released back in the day. It gave us a promise based wrapper around XMLHttpRequest, which was difficult to use. But that was a long time ago and times have changed — browsers have gotten smarter. Maybe it's time for your data fetching solution to keep up?

Thwack was built from the ground up with modern browsers in mind. Because of this, it doesn't have the baggage that Axios has. Axios weighs in at around ~5k gzipped. Thwack, on the other hand, is a slender ~1.5k.

They support the same API, but there are some differences — mainly around options — but for the most part, they should be able to be used interchangeably for many applications.

Thwack doesn't try to solve every problem, like Axios does, but instead provides the solution for 98% of what users really need. This is what gives Thwack its feather-light footprint.

Methods

Data fetching

• thwack(url: string [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.request(options: ThwackOptions): Promise<ThwackResponse>

• thwack.get(url: string [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.delete(url: string [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.head(url: string [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.post(url: string, data:any [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.put(url: string, data:any [,options: ThwackOptions]): Promise<ThwackResponse>;

• thwack.patch(url: string, data:any [,options: ThwackOptions]): Promise<ThwackResponse>;

Utility

• thwack.create(options: ThwackOptions): ThwackInstance;

  The create method creates (da!) a new child instance of the current Thwack instance with the given options.

• thwack.getUri(options: ThwackOptions): string;

Event listeners

Thwack supports the following event types: request, response, data, and error.

For more information on Thwack's event system, see Thwack events below.

• thwack.addEventListener(type: string, callback: (event:ThwackEvent) => Promise<any> ): void;

• thwack.removeEventListener(type: string, callback: (event:ThwackEvent) => Promise<any> ): void;

ThwackOptions

The options argument has the following properties.

url

This is either a fully qualified or a relative URL.

baseURL

Defines a base URL that will be used to build a fully qualified URL from url above. Defaults to the origin + pathname of the current web page.

For example, if you did this:

thwack('foo', {
  baseURL: 'http://example.com',
});

the fetched URL will be:

http://example.com/foo

method

A string containing one of the following HTTP methods: get, post, put, patch, delete, or head.

data

If the method is post, put, or patch, this is the data that will be used to build the request body.

headers

This is where you can place any optional HTTP request headers. Any header you specify here are merged in with any instance header values.

For example, if we set a Thwack instance like this:

const api = thwack.create({
  headers: {
    'x-app-name': 'My Awesome App',
  },
});

Then later, when you use the instance, you make a call like this:

const { data } = await api.get('foo', {
  headers: {
    'some-other-header': 'My Awesome App',
  },
});

The headers that would be sent are:

x-app-name: My Awesome App
some-other-header': 'My Awesome App'

defaults

This allows you to read/set the default options for this instance and, in effect, any child instances.

Example:

thwack.defaults.baseURL = 'https://example.com/api';

For an instance, defaults is the same object passed to create. For example, the following will output "https://example.com/api".

const instance = thwack.create({
  baseURL: 'https://example.com/api',
});
console.log(instance.defaults.baseURL);

params

This is an optional object that contains the key/value pairs that will be used to build the fetch URL. Is there are any :key segments of the baseURL or the url, they will be replaced with the value of the matching key. For example, if you did this:

thwack('orders/:id', {
  params: { id: 123 },
  baseURL: 'http://example.com',
});

the fetched URL will be:

http://example.com/orders/123

If you don't specify a :name, or there are more params than there are :names, then the remaining key/values will be set as search parameters (i.e. ?key=value).

maxDepth

The maximum level of recursive requests that can be made before Thwack throws an error. This is used to prevent a event callback from causing a recursive loop if it issues another request without proper guards in place. Default = 5.

responseType

By default, Thwack will automatically determine how to decode the response data based on the value of the response header content-type. However, if the server responds with an incorrect value, you can override the parser by setting responseType. Valid values are arraybuffer, document (i.e. formdata), json, text, stream, and blob. Defaults to automatic.

What is returned by Thwack is determined by the following table. The "fetch method" column is what is resolved in data. If you do not specify a responseType, Thwack will automatically determine the fetch method based on content-type and the responseParserMap table (see below).

responseParserMap

Another useful way to determine which response parser to use is with responseParserMap. It allows you to set up a mapping between content types and parser types.

Thwack uses the following map as the default, which allows json and formdata decoding. If there are no matches, the response parser defaults to text. You may specify a default by setting the special */* key.

{
  "application/json": "json",
  "multipart/form-data": "formdata",
  "*/*": "text"
};

Any value you specify in responseParserMap is merged into the default map. That is to say that you can override the defaults and/or add new values.

Let's say, for example, you would like to download an image into a blob. You could create an instance of Thwack (using thwack.create()) and share it throughout your entire application. Here we set the baseURL to our API endpoint and a responseParserMap that will download images of any type as blobs, but will still allow json downloads (as this is the default for a content-type: application/json).

// api.js
import thwack from 'thwack';

export default thwack.create({
  responseParserMap: { 'image/*': 'blob' },
});

Then import the api.js file to use these options in other parts of your application. Any URL that you download with an image/* content type (e.g. image/jpeg, image/png, etc) will be parsed with the blob parser.

import api from './api';

const getBlobUrl = async (url) => {
  const blob = (await api.get(url)).data;
  const objectURL = URL.createObjectURL(blob);
  return objectURL;
};

See this example running on CodeSandbox.

Note that this works for other things besides images.

As you can see, using responseParserMap is a great way to eliminate the need to set responseType for different Thwack calls.

ThwackResponse

status

A number representing the 3 digit HTTP status codes that was received.

• 1xx - Informational response
• 2xx - Success
• 3xx - Redirection
• 4xx - Client errors
• 5xx - Server errors

ok

A boolean set to true is the status code in the 2xx range (i.e. a success). If the promise resolves successfully, this value will always be true. If the request has a status outside of the 2xx range Thwack will throw a ThwackResponseError and ok will be false.

statusText

A string representing the text of the status code. You should use the status code (or ok) in any program logic.

headers

A key/value object with the returned HTTP headers. Any duplicate headers will be concatenated into a single header separated by semicolons.

data

This will hold the returned body of the HTTP response after it has been streamed and converted. The only exception is if you used the responseType of stream, in which case data is set directly to the body element.

If a ThwackResponseError was thrown, data will be the plain text representation of the response body.

options

The complete options object that processed the request. This options will be fully merged with parent instances (if any) as well as with defaults.

response

The complete HTTP Response object as returned by fetch.

ThwackResponseError

If the response from a Thwack request results in a non-2xx status code (e.g. 404 Not Found) then a ThwackResponseError is thrown.

Note: It is possible that other types of errors could be thrown (e.g. a bad event listener callback), so it is a best practice to interrogate the caught error to see if it is of type ThwackResponseError.

try {
  const { data } = await thwack.get(someUrl)
} catch (ex) {
  if (ex instanceof thwack.ThwackResponseError)
    const { status, message } = ex;
    console.log(`Thwack status ${status}: ${message}`);
  } else {
    throw ex; // If not, rethrow the error
  }
}

A ThwackResponseError has all of the properties of a normal JavaScript Error plus a thwackResponse property with the same properties as a success status.

Instances

Instances created in Thwack are based on the parent instance. A parent's default options pass down through the instances. This can come in handy for setting up options in the parent that can affect the children, such as baseURL,

Inversely, parents can use addEventListener to monitor their children (see the How to log every API call below for an example of this).

Thwack events

Combined with instances, the Thwack event system is what makes Thwack extremely powerful. With it, you can listen for different events.

Here is the event flow for all events. AS you can see, it is possible for your code to get into an endless loop, should your callback blindly issue a request() without checking to see if it's already done so, so take caution.

The request event

Whenever any part of the application calls one of the data fetching methods, a request event is fired. Any listeners will get a ThwackRequestEvent object which has the options of the call in event.options. These event listeners can do something as simple as (log the event) or as complicated as preventing the request and returning a response with (mock data)

// callback will be called for every request made in Thwack
thwack.addEventListener('request', callback);

Note that callbacks can be async allowing you to defer Thwack so that you might, for example, go out and fetch data a different URL before proceeding.

The response event

The event is fired after the HTTP headers are received, but before the body is streamed and parsed. Listeners will receive a ThwackResponseEvent object with a thwackResponse key set to the response.

The data event

The event is fired after the body is streamed and parsed. It is fired only if the fetch returned a 2xx status code. Listeners will receive a ThwackDataEvent object with a thwackResponse key set to the response.

The error event

The event is fired after the body is streamed and parsed. It is fired if the fetch returned a non-2xx status code. Listeners will receive a ThwackErrorEvent object with a thwackResponse key set to the response.

NodeJS

Thwack will work on NodeJS, but requires a polyfill for window.fetch. Luckily, there is a wonderful polyfill called node-fetch that you can use.

If you are using NodeJS version 10, you will also need a polyfill for Array#flat and Object#fromEntries. NodeJS version 11+ has these methods and does not require a polyfill.

You can either provide these polyfills yourself, or use one of the following convenience imports instead. If you are running NodeJS 11+, use:

import thwack from 'thwack/node'; // NodeJS version 11+

If you are running on NodeJS 10, use:

import thwack from 'thwack/node10'; // NodeJS version 10

Note: The responseType of blob is not supported on NodeJS.

How to

Cancelling a request

Use an AbortController to cancel requests by passing its signal in the thwack options:

const controller = new AbortController();
const { signal } = controller;

thwack(url, { signal }).then(handleResponse).catch(handleError);

controller.abort();

In case you want to perform some action on request cancellation, you can listen to the abort event on signal too:

signal.addEventListener('abort', handleAbort);

Log every request

Add an addEventListener('request', callback) and log each request to the console.

import thwack from 'thwack';

thwack.addEventListener('request', (event) => {
  console.log('hitting URL', thwack.getUri(event.options));
});

If you are using React, here is a Hook that you can "use" in your App that will accomplish the same thing.

import { useEffect } from 'react';
import thwack from 'thwack';

const logUrl = (event) => {
  const { options } = event;
  const fullyQualifiedUrl = thwack.getUri(options);
  console.log(`hitting ${fullyQualifiedUrl}`);
};

const useThwackLogger = () => {
  useEffect(() => {
    thwack.addEventListener('request', logUrl);
    return () => thwack.removeEventListener('request', logUrl);
  }, []);
};

export default useThwackLogger;

Here is a code snippet on how to use it.

const App = () ={
  useThwackLogger()

  return (
    <div>
      ...
    </div>
  )
}

Return mock data

Let's say you have an app that has made a request for some user data. If the app is hitting a specific URL (say users) and querying for a particular user ID (say 123), you would like to prevent the request from hitting the server and instead mock the results.

The status in the ThwackResponse defaults to 200, so unless you need to mock a non-OK response, you only need to return data.

thwack.addEventListener('request', async (event) => {
  const { options } = event;
  if (options.url === 'users' && options.params.id === 123) {
    // tells Thwack to use the returned value instead of handling the event itself
    event.preventDefault();

    // stop other listeners (if any) from further processing
    event.stopPropagation();

    // because we called `preventDefault` above, the caller's request
    // will be resolved to this `ThwackResponse` (defaults to status of 200)
    return new thwack.ThwackResponse({
      data: {
        name: 'Fake Username',
        email: 'fakeuser@example.com',
      },
    });
  }
});

Convert DTO to Model

Often it is desirable to convert a DTO (Data Transfer Object) into something easier to consume by the client. In this example below, we convert a complex DTO into firstName, lastName, avatar, and email. Other data elements that are returned from the API call are ignored.

You can see an example of DTO conversion, logging, and returning fake data in this sample app.

You can view the source code on CodeSandbox.

Load an Image as a Blob

In this example, we have a React Hook that loads an image as a Blob URL. It caches the URL to Blob URL mapping in session storage. Once loaded, any refresh of the page will instantaneously load the image from Blob URL.

const useBlobUrl = (imageUrl) => {
  const [objectURL, setObjectURL] = useState('');

  useEffect(() => {
    let url = sessionStorage.getItem(imageUrl);

    async function fetchData() {
      if (!url) {
        const { data } = await thwack.get(imageUrl, {
          responseType: 'blob',
        });
        url = URL.createObjectURL(data);
        sessionStorage.setItem(imageUrl, url);
      }
      setObjectURL(url);
    }

    fetchData();
  }, [imageUrl]);

  return objectURL;
};

See this example on CodeSandbox

Selective routing

Right now you have a REST endpoint at https://api.example.com. Suppose you've published a new REST endpoint o a different URL and would like to start slowly routing 2% of network traffic to these new servers.

Note: normally this would be handled by your load balancer on the back-end. It's shown here for demonstration purposes only.

We could accomplish this by replacing options.url in the request event listener as follows.

thwack.addEventListener('request', (event) => {
  if (Math.random() >= 0.02) {
    return;
  }

  // the code will be executed for approximately 2% of the requests
  const { options } = event;
  const oldUrl = thwack.getUri(options);
  const url = new URL('', oldUrl);
  url.origin = 'https://api2.example.com'; // point the origin at the new servers
  const newUrl = url.href; // Get the fully qualified URL
  event.options = { ...event.options, url: newUrl }; // replace `options`]
});

Credits

Thwack is heavily inspired by the Axios. Thanks Matt!

License

Licensed under MIT

Contributors ✨

Thanks goes to these wonderful people (emoji key):

Donavon West 🚇 ⚠️ 💡 🤔 🚧 👀 🔧 💻	Jeremy Tice 📖	Yuraima Estevez 📖	Jeremy Bargar 📖	Brooke Scarlett Yalof 📖	Karl Horky 📖	Koji 📖 💻
Tom Byrer 📖	Ian Sutherland 💻	Blake Yoder 💻

This project follows the all-contributors specification. Contributions of any kind welcome!