GraalJS as an alternate to bun

[ivan-velikanov]

For a long time I've wondered: could GraalVM compete with Bun? This feels more relevant now that Bun was acquired by Anthropic.

Using Claude Code on Bun, I noticed it's memory-heavy but produces nice single executables. Bun's bun build feels cleaner than GraalVM's native-image (no MSVC dependency on Windows).

I've also wondered: could there be a polyglot GraalVM tool like Bun - not just for Node.js but Python and Java too? A "GUN" (GraalVM Universal Node... just kidding 😄). With all that polyglot/AOT power, where does GraalVM head if not providing better alternatives?

Disclaimer: These benchmarks were generated with AI assistance (Claude). While I monitored and corrected issues along the way, I'm not an expert - please take results with appropriate skepticism!

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Quick Observations

• Claude Code on Bun: ~400 MB RAM
• Claude Code on GraalVM: ~1200+ MB RAM

If GraalVM instances could share memory via CDS/AOT caching, this overhead might be justified. But currently it's significant.

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Benchmark Results Summary

Runtimes Tested (All with JIT warmup)

Rank	Runtime	Total Time	vs Java	Notes
🥇	Native Java JVM	~123ms	1.0x	Fastest overall
🥈	Native Bun	~211ms	1.7x	Fast startup, good perf
🥉	GraalVM Node	~534ms	4.3x	Polyglot tax
4	TeaVM WASM	~546ms	4.4x	Runs in browser
5	TeaVM JavaScript	~6033ms	49x	Translation overhead

Key Test Results (After Warmup)

Test	Java JVM	Bun	GraalVM	TeaVM WASM
Fibonacci (n=35)	39ms	95ms	196ms	182ms
Prime Numbers	1.2ms	1.3ms	1.5ms	2.6ms
Array Ops (1M)	1.1ms	19ms	120ms	5ms
Object Creation	9ms	19ms	14ms	2.3ms ⭐
Math Ops (1M)	~70ms	~70ms	87ms	88ms
Loop Perf (10M)	2.9ms	5.6ms	12ms	24ms

⭐ TeaVM WASM surprisingly beats everyone on object creation!

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GraalVM vs Bun Detailed Comparison

Cold Start

• Bun is ~26x faster on first run
• GraalVM suffers JVM startup penalty

After JIT Warmup (10+ iterations)

• Bun maintains 2.45x advantage
• GraalVM improves 91% but still trails
• GraalVM wins only Object Creation (28ms vs 50ms)

Consistency

• Bun wins 8/10 tests for lower variance
• GraalVM shows higher variance even warmed up

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Memory & Startup

Runtime	Memory	Startup
Java JVM	21 MB	727ms
Bun	142 MB	~0ms
GraalVM	535 MB	191ms

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My Humble Suggestions

1. GraalVM should benchmark against Bun, not just Node.js - Bun is the new performance bar

2. Consider TeaVM collaboration - TeaVM WASM performed surprisingly well (4.4x slower than Java, similar to GraalVM). Perhaps symbiotic development could benefit both projects? Just as Anthropic acquired Bun...

3. Java ecosystem is mature - Incremental JDK improvements are welcome but the exciting frontier is JavaScript/WASM. GraalVM's future outside JVM seems to be competing in that space

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Caveats

• All benchmarks AI-generated with human oversight
• Some corrections made along the way (e.g., caught a 118x math bug)
• TeaVM results puzzling - anecdotally feels faster than measured
• Your mileage may vary!

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Test Environment

• Java: JDK 25 HotSpot
• Bun: v1.3.0 (JavaScriptCore)
• GraalVM: Node v22.17.1
• TeaVM: 0.13.0
• Platform: Windows 11 x64

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TL;DR: Native Java JVM wins overall. Bun is 2.45x faster than GraalVM after warmup. TeaVM WASM is surprisingly competitive. Perhaps GraalVM could learn from or collaborate with these projects?

Benchmarks code and testing done with AI assistance - corrections and scepticism welcome!