backend-pe-javascript

name

backend-pe-javascript

description

Principal-engineer-grade JavaScript (non-TypeScript) backend design, implementation, and review. Covers Node 20+ LTS / Bun, modern ESM, runtime validation (Zod/Ajv), JSDoc types, Fastify/Hono/Express, Prisma/Drizzle, and JavaScript-specific failure modes (untyped boundaries, prototype pollution, async leaks, event-loop blocking). Use when designing, building, reviewing, refactoring, hardening, or debugging plain JavaScript backend services where adopting TypeScript is not an option. Trigger keywords - JavaScript backend, Node.js service, Fastify, Hono, ESM, Bun JavaScript, JSDoc types, Zod validation, Ajv, plain JS. Not for TypeScript code (use backend-pe-typescript), Node runtime internals (use backend-pe-nodejs), or frontend work.

JavaScript Backend Principal Engineer

Audience: Engineers designing, building, reviewing, or hardening plain JavaScript (non-TypeScript) backend services on Bun or Node 20+ LTS.

Goal: Principal-engineer-grade JavaScript - correctness maintained without a compiler, runtime validation at every boundary, JSDoc typing where it helps, and production hardening by default.

Priority Model

Correctness - Reliability - Security - Performance - Observability - Data consistency - Scalability - Developer experience. In that order.

Core Principles

1. Without TypeScript, runtime validation is not optional. Every external input - HTTP request, queue message, DB result, env var, file - parsed through Zod or Ajv before touching business logic. There is no compiler to catch a missing field or wrong type; the schema is the only source of truth.

2. JSDoc + checkJs gives you 70% of TypeScript at 0% migration cost. Add "checkJs": true in jsconfig.json, annotate public functions with JSDoc types, and VSCode + tsc --noEmit will catch most type bugs. Document why you chose plain JS over TS; if the reason evaporates, migrate.