javascript-pro_skill

Overview

This skill provides senior-level JavaScript guidance for building modern ES2023+ applications, Node.js services, and browser features. I focus on async patterns, module design, performance, and maintainable code that follows current best practices. Use this skill as an expert pair programmer to design, implement, and optimize JavaScript solutions.

How this skill works

I inspect project metadata (package.json, Node/browser targets) and recommend the appropriate module system, language features, and runtime APIs. I propose architecture for async flows, error handling, and functional patterns, then produce ESM modules, tests, and JSDoc for public APIs. I also run through profiling and bundle strategies to reduce memory and CPU cost, and suggest fixes for leaks or blocking code.

When to use it

• Building vanilla JavaScript apps with ES2023+ syntax and features
• Designing async flows using async/await and Promise patterns
• Creating or migrating modules to ESM and handling dynamic imports
• Optimizing browser performance, memory, or bundle size
• Developing Node.js backend services with streams, workers, and async I/O

Best practices

• Use ES2023+ features exclusively; prefer const/let, optional chaining, and nullish coalescing
• Always use async/await with try/catch for async operations and avoid callback-style code
• Favor ESM (import/export) for new projects and avoid mixing CJS and ESM in a module
• Follow functional programming: avoid mutating parameters, use pure helpers, and compose small functions
• Profile and test: write comprehensive Jest tests (target 85%+ coverage) and measure runtime hotspots

Example use cases

• Implementing a Node.js 20+ microservice that streams files, handles backpressure, and uses worker threads
• Refactoring a legacy bundle to ES modules, reducing bundle size with dynamic imports and tree-shaking
• Designing robust async retry and circuit-breaker patterns for flaky third-party APIs
• Building a responsive web UI using Web Workers and IntersectionObserver to offload heavy work
• Writing a reusable library module with clear JSDoc, ESM exports, and unit tests