JavaScript Engine Zoo – The Ultimate Comparison of Every JavaScript Engine

Quick take

• What it is – A publicly‑maintained table that scores every open‑source JavaScript engine on performance, binary size, age, language, JIT support, target platform, GitHub stars, contributors, and license.
• Why it matters – Choosing the right engine can shave megabytes off an IoT firmware, cut latency on a high‑traffic Node service, or keep your project legally safe.
• Who should care – Front‑end architects, backend engineers, embedded‑systems developers, and anyone who ships JavaScript outside the browser.

The zoo in a nutshell

The JavaScript Engine Zoo lives at https://zoo.js.org/ and lists every publicly available engine, from the heavyweight V8 to the feather‑weight QuickJS. Each entry gets an EngineScore that aggregates raw speed, binary footprint, lines of code, and community health. The table is openly editable, so new projects (e.g., Bun’s JavaScript VM) appear almost instantly.

The zoo isn’t just a curiosity; it’s a decision‑making toolkit. By scanning a single row you can answer questions like:

• “Which engine fits under 1 MB for an ESP32?” – QuickJS or Duktape.
• “What runs fastest on a 32‑core server?” – V8 with TurboFan.
• “Is the license MIT‑compatible?” – Check the License column (BSD for V8, MPL 2.0 for SpiderMonkey).

EngineScore demystified

EngineScore isn’t a mystical benchmark; it’s a weighted sum of:

The zoo’s authors give performance ~40 % of the weight, binary size ~20 %, and the remaining metrics share the rest. This balanced view prevents the classic “fastest‑but‑bulky” trap.

Who wins where? Top performers and niche champs

Heavy‑weight champions

• V8 (Chrome/Node) – Holds the highest EngineScore, thanks to TurboFan’s aggressive optimizations and a massive contributor base (≈2 k stars, 400+ contributors). Binary size is ~7 MB, but the speed gains on server‑side workloads are undeniable【2†L1-L3】.
• SpiderMonkey (Firefox) – MPL‑2.0 licensed, slightly slower than V8 but still a JIT powerhouse. It shines in environments that need tight integration with Mozilla’s tooling (e.g., Firefox OS).
• JavaScriptCore (Safari/WebKit) – Wins on binary size (≈4 MB) and tight coupling with WebKit, making it the default for Apple platforms. Its JIT is less aggressive than V8 but more than sufficient for mobile browsing【4†L1-L3】.

Tiny yet mighty

• QuickJS – Written in C, packs under 200 KB, and still supports ES2022 features. Perfect for IoT, sandboxed plugins, or CLI tools where every kilobyte counts【5†L1-L3】.
• Duktape – Even smaller (≈180 KB) and deliberately “no JIT” to keep memory usage predictable. Widely used in embedded routers and game scripting.

Pitfalls of chasing raw speed

1. Bloat vs. performance – Engines with a high EngineScore tend to have larger binaries and more lines of code, which translates into higher memory footprints and a larger attack surface. Deploying V8 on a low‑end ARM board can cause out‑of‑memory crashes.
2. License traps – V8’s BSD license is permissive, but SpiderMonkey’s MPL 2.0 imposes source‑code disclosure for modifications. Ignoring this can lead to unexpected compliance work.
3. Feature lag – Tiny engines like QuickJS skip JIT for size, meaning they may struggle with compute‑heavy loops. If your app does heavy number crunching, a “small” engine could become the bottleneck.

Best practices for picking an engine

1. Define the deployment context – Browser, Node, edge, or microcontroller? The target platform dictates the baseline (V8 for Node, JavaScriptCore for iOS, QuickJS for ESP32).
2. Score the trade‑offs – Use the zoo’s table to plot binary size against performance. A quick spreadsheet can reveal a “sweet spot” where size ≤ 500 KB and latency ≤ 2 ms for typical workloads.
3. Check community health – Engines with > 500 stars and regular commits are less likely to become abandonware. V8 and SpiderMonkey have weekly releases; QuickJS sees monthly patches, which is adequate for most embedded projects.
4. Validate license compatibility early – Add a compliance checklist to your CI pipeline; a mismatched license can halt a release at the last minute.
5. Prototype before you commit – Spin up a minimal benchmark (e.g., a factorial loop) on each candidate. The zoo’s EngineScore is a great starting point, but real code paths can expose hidden bottlenecks.

Real‑world use cases

Frequently asked questions

Q1: Does a higher EngineScore always mean better real‑world performance?
No. EngineScore balances speed with size, community, and licensing. For compute‑heavy workloads V8 often wins, but for a 64‑KB microcontroller QuickJS’s modest speed is a worthwhile trade‑off.

Q2: Can I embed V8 in a Rust or Go project?
Yes. V8 offers C++ APIs and there are community bindings for Rust (rusty_v8) and Go (v8go). Expect a binary size increase and a more complex build pipeline.

Q3: How often does the zoo get updated?
The repository behind https://zoo.js.org/ is refreshed on every major engine release. New entrants like Bun’s VM appear within days, while minor patches are added as contributors submit pull requests.

Q4: Are there security implications when using a JIT engine on IoT devices?
JIT compilation generates executable memory at runtime, which can be a vector for code‑injection attacks on devices without proper NX (no‑execute) enforcement. Tiny interpreters like QuickJS avoid this risk by staying interpreter‑only.

Q5: What’s the best way to stay current with ECMAScript feature support across engines?
Track the “ECMAScript Compatibility” column on the zoo page and subscribe to each engine’s release blog (V8 blog, Mozilla Hacks, WebKit Daily). Automated CI checks using core-js can also surface missing features early.

Choosing a JavaScript engine isn’t a one‑size‑fits‑all decision; it’s a balancing act between speed, size, license, and community vigor. The JavaScript Engine Zoo gives you a bird’s‑eye view, but the final call should always be grounded in the constraints of your product. Test, measure, and let the data—not hype—guide you to the perfect engine for the job.