# JeffJS — Quantum JavaScript Engine > JavaScript REPL for Apple devices with full ES2023 and browser runtime. (iPhone/iPad app by Hudson AI Platforms LLC.) - Source: https://appshunter.io/ios/app/jeffjs/id6763828438 (this page in markdown: same URL + `.md`) - Developer: [Hudson AI Platforms LLC](https://appshunter.io/developer/985846267) - Category: Utilities - Price: $0.99 - Rating: 5.00/5 from 1 App Store ratings - Age rating: 4+ - Requires: iOS 13.0 · 10 MB - Languages: English - Released: 2026-04-27 - Data updated: 2026-10-31 - Monetization: paid ## What is JeffJS? JeffJS Console is a real JavaScript REPL for every Apple device — iPhone, iPad, Mac, Apple Watch, and Vision Pro. Pure-Swift engine, full ES2023, browser-shaped runtime, even on your wrist. WHAT IT IS A scratchpad for JavaScript that runs anywhere Swift runs, powered by a 1:1 port of QuickJS — about 70,000 lines of Swift you could step through in Xcode. No JavaScriptCore. No FFI. No opaque blobs. Type code, run it, see results. LANGUAGE COVERAGE Full ES2023: • Classes, modules, generators, async/await • Destructuring, spread, template literals • Optional chaining, nullish coalescing • BigInt, Symbol, Proxy, WeakRef • TypedArrays, ArrayBuffer, DataView • RegExp with named capture groups, lookbehind, Unicode mode • Dynamic import() BROWSER SURFACE Boots a window/document/fetch world without wiring anything up: • window, document, console, performance, crypto • fetch, WebSocket, IndexedDB • localStorage, sessionStorage • setTimeout, setInterval, queueMicrotask • TextEncoder, TextDecoder, URL, structuredClone, atob, btoa • A real DOM — HTML parser, CSS selectors, events, mutation callbacks THE REPL ITSELF • Persistent user globals — your variables survive between sessions • Command history with up/down navigation • Inline ghost-text autocomplete • Dot-completion that introspects live objects • A keyboard accessory bar for JS-friendly characters • Light, dark, and tinted icon variants ON YOUR WRIST JavaScriptCore isn't available on watchOS. JeffJS is. The bundled Watch App runs the same engine with the same language coverage as the phone. The complications widget shows your most recent eval result on your watch face. BUILT FOR PERFORMANCE On Apple Silicon, hot paths lift onto the GPU: • The garbage collector dispatches three Metal compute kernels above ~5,000 live objects (trial-decref → scan-rescue → collect-dead) • The regex engine compiles patterns into a flat NFA and tests every starting position in parallel via Metal • CPU fallbacks mean nothing breaks where the GPU isn't available OPEN SOURCE JeffJS is MIT-licensed and developed in the open. The full source for the engine, the console UI, the watch app, the test suite, and the tooling lives at github.com/jeffbachand/JeffJS — not just the binary you're downloading. Issues, PRs, and discussion welcome. WHO IT'S FOR • Developers who want a real JS scratchpad in their pocket • Anyone learning JavaScript who wants to try things without firing up a browser • Engineers who've ever wanted to run a script on their watch • Curious people who want to read how a JavaScript engine actually works my name is jeff. ## Key features - Full ES2023 JavaScript support - Browser-shaped runtime (window, document, fetch) - Persistent user globals - Command history and autocomplete - Keyboard accessory bar - Apple Watch app and complications - GPU acceleration for performance ## Is JeffJS safe? Not enough ratings yet to assess JeffJS. ## Is JeffJS legit? JeffJS appears legitimate, with a few gaps. The AppsHunter Legitimacy Score for JeffJS is 60 out of 100 points across 7 verification signals from App Store and developer data. ## Frequently asked questions about JeffJS ### What devices does JeffJS support? JeffJS is available on iPhone, iPad, Apple Watch, Mac, and Vision Pro. The app leverages Swift's cross-platform capabilities to run the same engine across these devices. ### What JavaScript features does JeffJS support? JeffJS offers full ES2023 support, including classes, modules, async/await, destructuring, optional chaining, BigInt, Symbol, Proxy, and dynamic import(). It also includes advanced features like RegExp with named capture groups. ### Does JeffJS have ads? No, JeffJS is ad-free. As a paid application, it provides an uninterrupted experience for users. ### How much does JeffJS cost? JeffJS is a paid application priced at $0.99. This one-time purchase grants access to all features and future updates. ### How often is JeffJS updated? The latest version, 1.0, was released on April 28, 2026, with the initial release on April 27, 2026. Updates are likely to follow based on developer activity and user feedback. ### Is JeffJS suitable for beginners learning JavaScript? Yes, JeffJS is excellent for anyone learning JavaScript. It allows users to experiment with code directly on their devices without needing a full development environment. ### Can I run JavaScript on my Apple Watch with JeffJS? Absolutely. JeffJS includes a dedicated Watch App that runs the same engine as the phone version, allowing you to execute JavaScript directly on your wrist. It even features complications to display recent eval results. ### What makes JeffJS's engine unique? JeffJS uses a pure-Swift engine, a 1:1 port of QuickJS, avoiding JavaScriptCore or FFI. It offers a browser-shaped runtime with features like `window`, `document`, and `fetch` available out-of-the-box. ## Version history (last 1 release) ### 1.0 — 2026-04-28 No release notes. ## More apps by Hudson AI Platforms LLC - [Threesday](https://appshunter.io/ios/app/threesday/id6479314145) - [JeffJS Console](https://appshunter.io/ios/app/jeffjs-console/id6763829201) All apps by Hudson AI Platforms LLC: https://appshunter.io/developer/985846267 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-31.*