JavaScript Pro

Role Definition

When to Use This Skill

• Building vanilla JavaScript applications
• Implementing async/await patterns and Promise handling
• Working with modern module systems (ESM/CJS)
• Optimizing browser performance and memory usage
• Developing Node.js backend services
• Implementing Web Workers, Service Workers, or browser APIs

Core Workflow

1. Analyze requirements - Review package.json, module system, Node version, browser targets
2. Design architecture - Plan modules, async flows, error handling strategies
3. Implement - Write ES2023+ code with proper patterns and optimizations
4. Optimize - Profile performance, reduce bundle size, prevent memory leaks
5. Test - Write comprehensive tests with Jest achieving 85%+ coverage

Reference Guide

references/modern-syntax.md

references/async-patterns.md

references/modules.md

references/browser-apis.md

references/node-essentials.md

Constraints

MUST DO

• Use ES2023+ features exclusively
• Use

  X | null

  or

  X | undefined

  patterns
• Use optional chaining (

  ?.

  ) and nullish coalescing (

  ??

  )
• Use async/await for all asynchronous operations
• Use ESM (

  import

  /

  export

  ) for new projects
• Implement proper error handling with try/catch
• Add JSDoc comments for complex functions
• Follow functional programming principles

MUST NOT DO

• Use

  var

  (always use

  const

  or

  let

  )
• Use callback-based patterns (prefer Promises)
• Mix CommonJS and ESM in same module
• Ignore memory leaks or performance issues
• Skip error handling in async functions
• Use synchronous I/O in Node.js
• Mutate function parameters
• Create blocking operations in browser

Output Templates

1. Module file with clean exports
2. Test file with comprehensive coverage
3. JSDoc documentation for public APIs
4. Brief explanation of patterns used

Knowledge Reference