While building JS/TS librairies for LiterateInk and Papillon, I had a lot of issues concerning compatibility across runtimes.

Let's see an example about Set-Cookie headers.

// Browsers, Bun, Deno, Node.js
new Headers([
  ["Set-Cookie", "hello=1"],
  ["Set-Cookie", "world=2"],
]).getSetCookie();
// This simply works, we get the following.
// > ["hello=1", "world=2"]

// React Native
new Headers([
  ["Set-Cookie", "hello=1"],
  ["Set-Cookie", "world=2"],
]).getSetCookie();
// This does NOT work because they're using
// https://www.npmjs.com/package/whatwg-fetch
// and `getSetCookie` is not implemented there.
// You can fix this by using the following code instead:
new Headers([
  ["Set-Cookie", "hello=1"],
  ["Set-Cookie", "world=2"],
]).get("Set-Cookie");
// > "hello=1, world=2"
// Now this works, but as you can see the output is not the same...
// We have to handle this properly !

So we have to use different code for React Native and the rest of the runtimes and also handle the fact that the output is not the same ! As you can see, this is very frustrating.

Now let's query an API that is not allowing CORS through Tauri.

// Tauri
const response = await fetch("https://api.example.com");
// > Error: CORS
// To fix this issue, you have to instead use the
// `fetch` API from official Tauri plugins.

// Node.js, Bun, Deno, React Native
const response = await fetch("https://api.example.com");
// > 200 OK
// Simply works !

Now you can see that the CORS policy is not the same across runtimes. It's completely normal and compliant behavior, but it can be frustrating when you want to build a cross-platform library that should work everywhere.

Note that you should really only use this library if you want to build a cross-platform library which needs to either interact with Set-Cookie headers (such as Set-Cookie), either manipulate request headers (such as User-Agent, Origin or Referer) or simply ignore CORS.

The goal of this library is to provide a consistent API across runtimes. This means that you can use the same HTTP API across all runtimes, and it will behave the same way.

• Implements a working getSetCookie function on HeaderMap, even on React Native
• Tauri's native HTTP plugin is automatically used when available
• Uses undici on Bun to prevent strange headers issues
• Provides optional toXML() and toHTML() helpers in HttpResponse for easier access with other packages, see installation section to enable those
• Uses a native implementation of fetch on React Native

pnpm add schwi

bun add schwi undici

You should setup Tauri's HTTP plugin first, see https://tauri.app/plugin/http-client/ for more details.

pnpm tauri add http
pnpm add schwi

react-native-real-fetch is required to use features that are not supported by the default fetch implementation in React Native. react-native-nitro-modules is required to build react-native-real-fetch properly.

npm add schwi react-native-real-fetch react-native-nitro-modules
cd ios && pod install

npx expo add react-native-real-fetch react-native-nitro-modules
npm add schwi
npx expo prebuild

# Enables `HttpResponse.toHTML()`, otherwise you'll get an error during runtime.
pnpm add cheerio

# Enables `HttpResponse.toXML()`, otherwise you'll get an error during runtime.
pnpm add fast-xml-parser

import { HttpRequest, send } from "schwi";

const request = new HttpRequest.Builder("https://postman-echo.com/cookies/set")
  .setUrlSearchParameter("foo1", "bar1")
  .setUrlSearchParameter("foo2", "bar2")
  .setRedirection(HttpRequest.Redirection.MANUAL)
  .build();

const response = await send(request);
console.log(response.headers.getSetCookie());

const body = await response.toString();
console.log(body);

You can browse the examples folder to see how to use the library in different runtimes.