Fetsh

Fetsh helps you to establish contracts between your complex web app and all the different API it requires.

Installation

$ yarn add fetsh

Principles

Fetsh follows a simple rule: any route should be able to be defined with its own response parser. This could be called a contract between an URI and the response returned. Let's give an example:

// routing.ts
import {
  createUrlContract,
  jsonApiTransform,
  headers,
} from 'fetsh';

/**
* What if this API return 200 even if there is an error
* and you have to parse the payload to determine if the request returned an error or is on success
* (We all encountered legacy code or API...)
* @param response
*/
const adapterForLegacyAPI = (response: any) => {
  // Imagine your server return a key named `error` containing the error the server returned
  if(response.error){
    // You could simply throw an error and then where you call this route, you would be able to call catch on the promise
    throw new Error('Server Error special case');
  }
  
  // Or simply return your data or transform the data returned
  return response.data;
};

//After creating your adapter for a special API or route, create the contract

/**
* Here we want to return the array returned in the payload
*/
export const GET_MOVIES_FROM_REST_API = createUrlContract({
  url: 'https://mydomain.ext/api/movies',
  adapter: response => response.movies,
});

/**
* If you use JSON API
* https://jsonapi.org/
* Use the built-in adapter provided by Fetsh library
*/
export const GET_MOVIES_FROM_JSON_API = createUrlContract({
  url: 'https://mydomain.ext/jsonApi/movies',
  adapter: jsonApiTransform,
  contentType: headers.JSONAPI,
});

/**
* or use your own adapter for your legacy API
*/
export const GET_MOVIES_FROM_LEGACY_API = createUrlContract({
  url: 'https://mydomain.ext/legacyApi/movies',
  adapter: adapterForLegacyAPI,
});

// app.ts
import {
  get,
  parametize,
  parametizeFetch,
} from 'fetsh';
import {
  GET_MOVIES_FROM_REST_API,
  GET_MOVIES_FROM_JSON_API,
  GET_MOVIES_FROM_LEGACY_API,
} from './routing.js';

get(GET_MOVIES_FROM_REST_API).then((movies: any[]) => {
  // do whatever you want with your data
});

get(GET_MOVIES_FROM_JSON_API).then((movies: any[]) => {
  // the data went through the json api adapter so they are properly formated
  // do whatever you want with your data
});

get(GET_MOVIES_FROM_LEGACY_API).then((movies: any[]) => {
  // the data went through your custom legacy adapter so they are properly formated
  // do whatever you want with your data
});

By simply doing this, you can deal with many different REST API endpoints that may return data with different shape, by establish a contract in your routing file. This way, all your API call are defined in a single file. It is more readable and convenient for the developers and you can easily see how the data is transformed.

How to use

For all available http methods you will have to provide an UrlContract. You can also provide parameters depending on the need.

parametise

This helper must be used to compose all the parameters needed for your request. For some helpers like parametizeUrl, errors can be thrown if any parameter is not defined, making your app more secured.

parametizeUrl: when you define your contract, you provide an url. This url may need to add an id in the url path. For example you wanna fetch a specific resource with its ID: the url would looks like https://api.domain.com/movies/12345. You just have to surround any variable like this: ${variable} Using this helper, you will be protected from bad parameters and instead of querying https://api.domain.com/movies/undefined, it will throw an error on runtime telling you that one parameter is missing.

// routing.js
import {
  createUrlContract,
} from 'fetsh';

// you will define your contract like this
const GET_MOVIE = createUrlContract({
  url: 'https://api.domain.com/movies/${id}'
});


// app.js
import {
  get,
  parametize,
  parametizeUrl,
} from 'fetsh';
import {
  GET_MOVIE,
} from './routing.js'

// declare your url parameters
const urlParameters = parametizeUrl({
  id: 12345,
});

// request the server
get(GET_MOVIE, parametize(urlParameters));

parametizeQuery: Your url may also need query params, here is how to add some:

// routing.js
import {
  createUrlContract,
} from 'fetsh';

// you will define your contract like this
const GET_MOVIE = createUrlContract({
  url: 'https://api.domain.com/movies/${id}'
});


// app.js
import {
  get,
  parametize,
  parametizeUrl,
  parametizeQuery,
} from 'fetsh';
import {
  GET_MOVIE,
} from './routing.js'

// declare your url parameters
const urlParameters = parametizeUrl({
  id: 12345,
});
// declare your url query parameters
const queryParameters = parametizeQuery({
  rating: 5,
});

// request the server
get(GET_MOVIE, parametize(urlParameters, queryParameters));

and you will request https://api.domain.com/movies/12345?rating=5

parametizeBody: Use this helper if you wanna post data to the server

// routing.js
import {
  createUrlContract,
} from 'fetsh';

// you will define your contract like this
const CREATE_MOVIE = createUrlContract({
  url: 'https://api.domain.com/movies'
});


// app.js
import {
  post,
  parametize,
  parametizeBody,
} from 'fetsh';
import {
  CREATE_MOVIE,
} from './routing.js'

// declare your url parameters
const body = parametizeBody({
  name: 'Interstellar',
  rating: 5
});

// request the server
post(CREATE_MOVIE, parametize(body));

parametizeFetch: Use this helper if you wanna add custom fetch options like headers etc. The parameters are the same than for fetch, plus 2 extra options: isCrossDomain, to quickly specify in the request that you call a cross domain API and useCredentials to send your access_token througth cookie for example.

API

createUrlContract (object) => UrlContract: Creates a contract

it takes an object as parameter

Property	Type	Required	Description
url	string	true	the API endpoint url
adapter	function	false	Your custom result payload adapter
contentType	string	false	You can quickly specify what content type is expected for this route

parametize (ParametizeParameters, ...ParametizeParameters[]) => RequestParameters: compose your request parameters type ParametizeParameters = UrlParameters | QueryParameters | BodyParameters | FetchParameters; it takes one, to many ParametizeParameters as arguments

headers object: hashmap containing different types of headers (see source code for the complete list)

parametizeUrl (object) => UrlParameters: Returns the url parameter to be passed in parametize method.

parametizeQuery (object) => QueryParameters: Returns the query parameters to be passed in parametize method.

parametizeBody (object) => BodyParameters: Returns the body content to be passed in parametize method for any post, patch,put request.

parametizeFetch (object) => FetchParameters: Returns the fetch parameters to be passed in parametize method. This is the same api than fetch. https://developer.mozilla.org/fr/docs/Web/API/Fetch_API

get - post - put - patch - del (UrlContract, ParametizeParameters?) => Promise: send a request with fetch