jallab

A lightweight, environment-agnostic fetch wrapper with a powerful middleware system.

jallab allows you to intercept and modify requests and responses globally, enabling complex behaviors like authentication, logging, caching, and error handling with a simple, chainable API. It works wherever fetch is available (Browser, Node.js, Edge, Deno).

Features

• 🌍 Environment Agnostic: Works in Browsers, Node.js (v18+), Cloudflare Workers, Deno, etc.
• 🧅 Middleware System: Intercept requests and responses with an "onion" style execution chain (similar to Koa/Express).
• ⚡ Async/Await Support: Fully supports asynchronous operations in middleware (e.g., token refresh).
• 🛡️ Type Safe: Written in TypeScript with complete type definitions.
• 📦 Zero Dependencies: Extremely lightweight.

Installation

pnpm add jallab
# or
npm install jallab
# or
yarn add jallab

Usage

Basic Example

import createFetch from "jallab";

const fetch = createFetch();

// Add a logging middleware
fetch.use(async (context, next) => {
  console.log(`Requesting: ${context.request.url}`);
  const response = await next();
  console.log(`Response status: ${response.status}`);
  return response;
});

// Use it just like standard fetch
const response = await fetch("https://api.example.com/data");

Managing Middleware

You can add and remove middleware dynamically. Middleware functions are registered only once; subsequent calls to .use() with the same function will be ignored.

const fetch = createFetch();

const customHeaderMiddleware = async (ctx, next) => {
  ctx.request.headers.set("X-Custom", "123");
  return next();
};

// Add middleware
fetch.use(customHeaderMiddleware);

// Remove middleware using the same function reference
fetch.eject(customHeaderMiddleware);

Initial Middlewares

You can also provide a set of middlewares at initialization.

import createFetch from "jallab";

// Example: Performance logging middleware for development
const performanceLogger = async (ctx, next) => {
  const start = Date.now();
  const response = await next();
  const duration = Date.now() - start;

  if (duration > 3000) {
    console.error(`🔴 Critical Slowness: ${ctx.request.url} took ${duration}ms`);
  } else if (duration > 1000) {
    console.warn(`🟡 Slow Request: ${ctx.request.url} took ${duration}ms`);
  }

  return response;
};

const isDev = process.env.NODE_ENV === "development";

const fetch = createFetch({
  middlewares: [
    isDev && performanceLogger
  ]
});

API

createFetch(options?)

Creates a new fetch instance.

Parameters:

• options: CreateFetchOptions (Optional)
  • middlewares: (Middleware | boolean | null | undefined)[] - Initial set of middlewares. Falsy values are ignored.

Returns: A function that behaves like the standard fetch API, but with use and eject methods attached.

fetch.use(middleware)

Registers a middleware function. If the function is already registered, it does nothing.

Parameters:

• middleware: (context: Context, next: Next) => Promise<Response>

Returns: void

fetch.eject(middleware)

Removes a registered middleware by its function reference.

Parameters:

• middleware: (context: Context, next: Next) => Promise<Response>

Returns: void

Types

interface Context {
  request: Request;
}

type Next = () => Promise<Response>;

License

MIT