0.6.2 • Public • Published

Logo of Wayne library - it represent constrution worker helmet and text with the name of the library

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Service Worker Routing library for in browser HTTP requests

It's like Express inside Service Worker.

Most of the time Service Worker is used for caching of HTTP requests and making the app work when there is no internet (mostly for PWA), but in fact you can create completely new responses to requests that never leave the browser. This library make that easier by adding simple API similar to Express.


Installation from npm:

npm install @jcubic/wayne
yarn add @jcubic/wayne

Standard way of installing the service worker

if ('serviceWorker' in navigator) {
    const scope = location.pathname.replace(/\/[^\/]+$/, '/');
    navigator.serviceWorker.register('sw.js', { scope, type: 'module' })
             .then(function(reg) {
                 reg.addEventListener('updatefound', function() {
                     const installingWorker = reg.installing;
                     console.log('A new service worker is being installed:',
                 // registration worked
                 console.log('Registration succeeded. Scope is ' + reg.scope);
             }).catch(function(error) {
                 // registration failed
                 console.log('Registration failed with ' + error);

If you want to support browsers that don't support ES Modules in Service Worker use this instead:

if ('serviceWorker' in navigator) {
    const scope = location.pathname.replace(/\/[^\/]+$/, '/');
    navigator.serviceWorker.register('sw.js', { scope })
             .then(function(reg) {
                 reg.addEventListener('updatefound', function() {
                     const installingWorker = reg.installing;
                     console.log('A new service worker is being installed:',
                 // registration worked
                 console.log('Registration succeeded. Scope is ' + reg.scope);
             }).catch(function(error) {
                 // registration failed
                 console.log('Registration failed with ' + error);

Inside same file you can send AJAX requests with standard fetch API.

function get(url) {
      .then(res => res.text())
      .then(text => output.innerHTML = text);

input.addEventListener('click', () => {

error.addEventListener('click', () => {

Service worker - sw.js file

Importing Wayne module:

  • when worker created as ES Module
import { Wayne } from 'https://cdn.jsdelivr.net/npm/@jcubic/wayne';

const app = new Wayne();
  • When worker created as normal script

const app = new wayne.Wayne();

Using the library

const users = {
  1: 'Jakub T. Jankiewicz',
  2: 'John Doe',
  3: 'Jane Doe'

app.get('/user/{id}', function(req, res) {
  const user = users[req.params.id];
  if (user) {
    res.json({result: user});
  } else {
    res.json({error: 'User Not Found'});

app.get('/error', function(req, res) {

app.get('/redirect', function(req, res) {
  res.redirect(301, '/message');

app.get('/message', function(req, res) {
  res.text('Lorem Ipsum');

app.get('/external', function(req, res) {
  // lorem ipsum API

File system middleware

import { Wayne, FileSystem } from 'https://cdn.jsdelivr.net/npm/@jcubic/wayne';
import FS from "https://cdn.skypack.dev/@isomorphic-git/lightning-fs";
import mime from "https://cdn.skypack.dev/mime";
import path from "https://cdn.skypack.dev/path-browserify";

const { promises: fs } = new FS("__wayne__");

const app = new Wayne();

app.use(FileSystem({ path, fs, mime, prefix: '__fs__' }));

When not using a module the code will be similar. When you access URLS with prefix __fs__ like ./__fs__/foo it will read files from indexedDB file system named __wayne__. See Lightning-FS repo on details about the library.

RPC mechanism

In Service worker you create generic route that send data to broadcastChannel:

let id = 0;
const channel = new BroadcastChannel('rpc');

app.get('/rpc/{name}/*', function(req, res) {
    try {
        const current_id = ++id;
        const args = req.params[0].split('/');
        const payload = { id: current_id, method: req.params.name || 'ping', args };
        channel.addEventListener('message', function handler(message) {
            if (current_id == message.data.id) {
                channel.removeEventListener('message', handler);
    } catch(e) {

and in the main thread you create the other side of the channel and the remote methods:

const channel = new BroadcastChannel('rpc');

const methods = {
    ping: function() {
        return 'pong';
    sin: function(x) {
        return Math.sin(x);
    random: function() {
        return Math.random();
    json: function() {
        return fetch('https://api.npoint.io/8c7cc24b3fd405b775ce').then(res => res.json());

channel.addEventListener('message', async function handler(message) {
    if (Object.keys(message.data).includes('method', 'id', 'args')) {
        const { method, id, args } = message.data;
        try {
            const result = await methods[method](...args);
            channel.postMessage({id, result});
        } catch(error) {
            channel.postMessage({id, error});

When you send request /rpc/ping you will get response from methods.ping function.

  .then(res => res.text())
  .then(text => {
     console.log({ text });

With this setup, you can create new functions/methods that will map to HTTP requests.

The demo below uses random request:

let index = 0;
const requests = [

rpc.addEventListener('click', () => {
    get(random_request() );

function random_request() {
    const next_index = index++ % requests.length;
    return requests[next_index];

Server-Sent Events

Server-Sent Events is the way to stream data in the browser. It's native browser implementation of Long Polling. Here is example how to use SSE with Wayne:

Service Worker

app.get('/sse', function(req, res) {
  const stream = res.sse({
    onClose() {
  var timerId = setInterval(function() {
    const now = (new Date()).toString();
    stream.send({ data: now });
  }, 1000);

Main tread

let see_source;

sse_start.addEventListener('click', () => {
    see_source = new EventSource("./sse");
    see_source.onmessage = event => {

sse_stop.addEventListener('click', () => {
    if (see_source) {
        see_source = null;


API reference

Wayne object has those methods that correspond to HTTP methods

  • get
  • post
  • put
  • delete
  • patch

each method accepts URL with markers inside curly brackets those markers will be available from Request.params object. Request object is browser native object of a given request see MDN for details. The only change to the native API is that the object have proeprty params.

Here are few most important Request properties:

  • headers - Headers object to get key/value pairs use Object.fromEntires(req.headers.entries()).
  • method - request method as string.
  • url - string with full URL.
  • referrer - HTTP referer.
  • arrayBuffer() - Returns a promise that resolves with an ArrayBuffer representation of the request body.
  • blob() - Returns a promise that resolves with a Blob representation of the request body.
  • formData() - Returns a promise that resolves with a FormData representation of the request body.
  • json() - Returns a promise that resolves with the result of parsing the request body as JSON.
  • text() - Returns a promise that resolves with a text representation of the request body.

Response object is instance of HTTPResponse those have methods:

  • html()
  • json()
  • text()
  • send()

each of those methods accepts string as first argument. Second argument are options:

  • headers - any headers as key value pairs or you can pass Headers object.
  • statusText - The status message associated with the status code, e.g., OK.
  • status - The status code for the response, e.g., 200.
  • type - Content-Type of the response (MIME).

Additional methods:

  • redirect() - accept url or optional first argument that is number of HTTP code

Application also have middlewere as in Express.js

  • use(function(err, req, res, next) {}) 4 parameters it's error handler
  • use(function(req, res, next) {}) 3 parameters it's middlewere


The idea of using a Service worker to serve pure in browser HTTP requests has a long history. I've first used this technque for my Git Web Terminal and described the usage of it in the article from 2018: How to create Web Server in Browser. In June 2022, I came up with a cool new way of using this technique. While creating PoC for the article I'm going to write (will update this story when ready), I realized that I can extract all the logic of creating those fake HTTP requests into a library. This is how Wayne was born.

The name of the library was inspired by the scene in Wayne's World 2 in which Wayne dresses up as a construction worker.

Watch the video

I hightly recommend both movies if you haven't seen them already.


If you have any ideas for an improvement don't hesitate to create an issue. Code contributions are also welcome.

Working on your first Pull Request? You can learn how from this free series How to Contribute to an Open Source Project on GitHub

Article about or mention Wayne




Released with MIT license
Copyright (c) 2022-2023 Jakub T. Jankiewicz


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