Use Modern JavaScript + TypeScript

Produce predictable, type-safe, maintainable JS/TS with function-first design, strict defaults, and modern platform APIs. Never write fallback code for older runtimes or browsers.

Baseline

• TypeScript 5.9+, Node.js 24+, ESM only.
• Evergreen browsers: Chrome 146+, Firefox 148+, Safari 26+.
• React 19+ and Next.js 16+ App Router when relevant.
• No polyfills, no CommonJS, no legacy transpilation, no compatibility branches.

Reference Routing

Load only what the task needs:

• references/style-safety-and-correctness.md — tsconfig, type modeling examples, modern API usage examples, erasable TS table.
• references/performance-and-lazy-evaluation.md — lazy evaluation, iterator helpers, concurrency, compiler perf.
• references/pitfalls-and-anti-patterns.md — anti-pattern → fix lookup table.
• references/source-basis.md — canonical source provenance.