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JSSE: First JavaScript Engine to Pass 100% of test262 — Built Entirely by Claude Code in YOLO Mode
JSSE (JavaScript Simple Engine) became the first JavaScript engine to pass all 98,426 test262 non-staging test scenarios across language, built-ins, annexB, and intl402. The entire engine is written in Rust, built from scratch by Claude Code running autonomously in YOLO mode — the developer didn't write a single line of Rust or even create the GitHub repo manually. Rust was chosen specifically because its strict type system and compiler serve as a 'second feedback signal' alongside test262, letting the agent spend less time debugging. This is the strongest proof-of-concept for agent-built complex systems to date.
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