custom-fetch

Custom Fetch

Creates a function with the same API as WHATWG's fetch, but with your own custom behaviour. Ideal for testing or for modifying an HTTP request before sending.

import CustomFetch from 'custom-fetch';
import * as NodeFetch from 'node-fecth';

// You need to bring your own Request and Response constructors
// There are already libraries that implement these and I didn't want
// to re-implement them just for the sake of it.
const { Request, Response } = NodeFetch;

const fetch = new CustomFetch(async (request, signal) => {
    // `request` is an instance of the provided Request class,
    // constructed based on the arguments passed to `fetch`.
    // `signal` is the value of `signal` on the fetch options object
    // (or undefined if not provided)

    switch(request.url) {
        case 'http://horses.example/':
            // You can return just a response body and it will be
            // used as the first argument to the Response constructor
            return 'Welcome to horses.example';
        case 'http://flowers.example/foxglove.json':
            // You can also return a preconstructed Response object
            // (as long as it's of the same class as the given
            // Response constructor)
            return new Response(
                JSON.stringify({
                    name: 'Foxglove',
                    scientificName: 'Digitalis purpurea',
                    gbifId: 5414995
                }),
                {
                    headers: {
                        'Content-Type': 'application/json'
                    }
                }
            )
        default:
            // Since NodeFetch.fetch returns a Response object,
            // we can just forward the request on if we like,
            // or we could make modifications to the request
            // before doing so.
            request = new Request(request, { headers: { 'X-Favourite-Color': 'blue' } })
            return NodeFetch.fetch(request, { signal });
},
// Let CustomFetch know how to construct the request and response objects
{ Request, Response }
);

export default fetch('http://horses.example/');

Dependencies

None

custom-fetch

• custom-fetch
  • module.exports ⏏
    • new module.exports(fetchHandler, fetchConstructors)
    • ~Request : function
      • new Request(url, options)
    • ~Response : function
      • new Response(body, options)
    • ~fetchHandler ⇒ Response | string

module.exports ⏏

Custom Fetch constructor

Kind: Exported class

new module.exports(fetchHandler, fetchConstructors)

Param	Type	Description
fetchHandler	fetchHandler	Callback for handling fetch request.
fetchConstructors	object	Object containing constructors for creating fetch Request and Response classes
fetchConstructors.Request	Request	Constructor for a fetch Request object
fetchConstructors.Response	Response	Constructor for a fetch Response object

module.exports~Request : function

Kind: inner class of module.exports

new Request(url, options)

Param	Type
url	string
options	object

module.exports~Response : function

Kind: inner class of module.exports

new Response(body, options)

Param	Type
body	string
options	object

module.exports~fetchHandler ⇒ Response | string

Kind: inner typedef of module.exports

Param	Type
request	Request
signal	Signal