@windyroad/wrap-fetch NPM

@windyroad/wrap-fetch

@windyroad/wrap-fetch is a small library that provides a simple way to wrap the global fetch function with a custom wrapper function. This can be useful for adding custom headers to requests, caching responses, logging requests and responses, transforming responses, mocking responses for testing, adding authentication tokens to requests, handling errors, and more.

Installation

To install @windyroad/wrap-fetch, you can use npm or yarn:

npm install @windyroad/wrap-fetch

Usage

To use @windyroad/wrap-fetch, you can import the wrapFetch function and use it to wrap the global fetch function with a custom wrapper function. The wrapper function should take the fetch function and its arguments and return a promise that resolves to the response.

Here's an example of how to use wrapFetch to add custom headers to requests:

import { wrapFetch } from '@windyroad/wrap-fetch';

const wrapper = (fetchImpl, ...args) => {
  const headers = new Headers(args[1].headers);
  headers.set('Authorization', 'Bearer token');
  args[1].headers = headers;
  return fetchImpl(...args);
};

const wrappedFetch = wrapFetch(wrapper);
/**
 * Or 
 * ```
 * const wrappedFetch = wrapFetch(wrapper, customFetch);
 * ```
 * if you want to wrap a different implementation of fetch.
 **/

const url = 'https://example.com';
const options = { headers: { 'Content-Type': 'application/json' } };

const response = await wrappedFetch(url, options);

In this code, we've imported the wrapFetch function from @windyroad/wrap-fetch and used it to wrap the global fetch function with a function that adds an Authorization header to requests. We've then used the wrapped fetch function to make a request to https://example.com with a custom Content-Type header.

Examples

Here's a list of some useful examples of using @windyroad/wrap-fetch:

Adding custom headers to requests: You can use wrapFetch to add custom headers to requests by wrapping the fetch function with a function that adds the headers to the request.

const wrapper = (fetch, ...args) => {
  const headers = new Headers(args[1].headers);
  headers.set('Authorization', 'Bearer token');
  args[1].headers = headers;
  return fetch(...args);
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';
const options = { headers: { 'Content-Type': 'application/json' } };

const response = await wrappedFetch(url, options);

Caching responses: You can use wrapFetch to cache responses by wrapping the fetch function with a function that checks if the response is already cached and returns the cached response if it is.

const cache = new Map();
const wrapper = async (fetch, ...args) => {
  const key = JSON.stringify(args);
  if (cache.has(key)) {
    return cache.get(key);
  }
  const response = await fetch(...args);
  cache.set(key, response);
  return response;
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response1 = await wrappedFetch(url);
const response2 = await wrappedFetch(url);

Logging requests and responses: You can use wrapFetch to log requests and responses by wrapping the fetch function with a function that logs the request and response data.

const log = console.log.bind(console);
const wrapper = async (fetch, ...args) => {
  log('Request:', args);
  const response = await fetch(...args);
  log('Response:', response);
  return response;
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response = await wrappedFetch(url);

Transforming responses: You can use wrapFetch to transform responses by wrapping the fetch function with a function that transforms the response data before returning it.

const wrapper = async (fetch, ...args) => {
  const response = await fetch(...args);
  const data = await response.json();
  return { ...response, data };
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response = await wrappedFetch(url);

Mocking responses for testing: You can use wrapFetch to mock responses for testing by wrapping the fetch function with a function that returns a predefined response instead of making a real request.

const wrapper = async () => {
  return new Response('{"foo": "bar"}', { status: 200 });
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response = await wrappedFetch(url);

Adding authentication tokens to requests: You can use wrapFetch to add authentication tokens to requests by wrapping the fetch function with a function that adds the token to the request headers.

const token = 'secret';
const wrapper = (fetch, ...args) => {
  const headers = new Headers(args[1].headers);
  headers.set('Authorization', `Bearer ${token}`);
  args[1].headers = headers;
  return fetch(...args);
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response = await wrappedFetch(url);

Handling errors: You can use wrapFetch to handle errors by wrapping the fetch function with a function that checks for errors in the response and throws an error if one is found.

const wrapper = async (fetch, ...args) => {
  const response = await fetch(...args);
  if (!response.ok) {
    const data = await response.json();
    throw new Error(data.error);
  }
  return response;
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

await expect(wrappedFetch(url)).rejects.toThrow('Not found');

Adding query parameters to requests: You can use wrapFetch to add query parameters to requests by wrapping the fetch function with a function that adds the parameters to the request URL.

const wrapper = (fetch, ...args) => {
  const url = new URL(args[0]);
  url.searchParams.set('foo', 'bar');
  args[0] = url.toString();
  return fetch(...args);
};

const wrappedFetch = wrapFetch(wrapper);

const url = 'https://example.com';

const response = await wrappedFetch(url);

These examples should provide a good starting point for using @windyroad/wrap-fetch in your own projects.

API

`wrapFetch`

function wrapFetch<
  WrapInputs extends any[] = Parameters<typeof fetch>,
  WrapReturns = Awaited<ReturnType<typeof fetch>>,
  FetchFunction<Arguments, ResponseType> extends (...args: any) => Promise<any> = typeof fetch,
>(
  wrapper: (
    fetchImplInner: (
      ...args: FetchInputs<typeof fetchImpl>
    ) => Promise<FetchReturns<typeof fetchImpl>>,
    ...args: WrapInputs
  ) => Promise<WrapReturns>,
  fetchImpl?: FetchFunction<Arguments, ResponseType>,
): (...args: WrapInputs) => Promise<WrapReturns>

Wraps a fetch implementation with a wrapper function.

Parameters

wrapper: The wrapper function to apply to the fetch implementation.
fetchImpl: The fetch implementation to wrap. Defaults to the global fetch function.

Type Parameters

WrapInputs: The type of the input arguments for the wrapper function. Defaults to Parameters<typeof fetch>.
WrapReturns: The return type of the wrapper function. Defaults to Awaited<ReturnType<typeof fetch>>.
FetchFunction<Arguments, ResponseType>: The type of the fetch implementation. Defaults to typeof fetch.