sockts

A modern, browser-only SockJS client — rewritten in pure TypeScript ESM.

This is a fork of sockjs-client stripped down to what matters in 2025: a clean ESM module with zero dependencies, no Node.js runtime support, no legacy browser workarounds, and no CommonJS artifacts.

Why

The original sockjs-client was designed around 2011-era constraints: IE6/7/8 support, Node.js http fallback transports, CommonJS require(), and the debug npm package for logging. Over a decade later, every one of those concerns is obsolete for modern applications. This library removes them all and ships a small, type-safe ESM module instead.

What changed

Format & language

• Pure TypeScript ESM — no require(), no module.exports, no CommonJS
• export class / export function / export const throughout (no default exports)
• Arrow functions instead of const self = this patterns
• Template literals instead of string concatenation
• Date.now() instead of +new Date()
• "0".repeat(n) instead of new Array(n).join("0")
• Rest parameters instead of arguments object
• class extends instead of the inherits npm package
• Native URL constructor instead of url-parse npm package
• Native crypto.getRandomValues() instead of Node.js crypto.randomBytes()
• Project's own EventEmitter instead of Node.js events module
• console.log with namespace prefixes instead of the debug npm package

Node.js support removed

• No faye-websocket — uses browser WebSocket directly
• No eventsource npm package — uses browser EventSource directly
• No Node.js http/https-based XHR driver
• No shims.ts (ES5 polyfills for old browsers)
• No Node.js crypto — uses Web Crypto API

Legacy browser support removed

• No XDomainRequest (IE8-9) — deleted sender/xdr.ts, xdr-streaming.ts, xdr-polling.ts
• No ActiveXObject("htmlfile") — deleted receiver/htmlfile.ts, transport/htmlfile.ts, createHtmlfile() from utils/iframe.ts
• No ActiveXObject("Microsoft.XMLHTTP") fallback in XHR
• No IE HTTP status code normalization (1223→204, 12005/12029→0)
• No document.attachEvent / detachEvent fallbacks — addEventListener only
• No IE JSONP script.htmlFor / script.onclick hack
• No IE <iframe name="..."> createElement hack
• No script.onreadystatechange / iframe.onreadystatechange IE workarounds
• No Opera user-agent sniffing (isOpera())
• No Konqueror user-agent sniffing (isKonqueror())
• No Chrome packaged app detection (chrome.app.runtime)
• No CollectGarbage() IE COM hint
• No doc.parentWindow — IE-specific window reference
• No !(this instanceof Constructor) pattern (impossible with ES class)
• No protocols_whitelist deprecated option support

Dependencies removed

• debug — replaced with console.log namespaced calls
• eventsource — browser EventSource used directly
• faye-websocket — browser WebSocket used directly
• inherits — native class extends
• url-parse — native URL constructor

Building

bun run build

Outputs ESM bundle to dist/sockjs.js with TypeScript declarations via rolldown + tsc.

Testing

bun test

Type checking

bun run typecheck