Javascript Pro

JavaScript Pro

Core Workflow

1. Analyze requirements - Review package.json, module system, Node version
2. Design architecture - Plan modules, async flows, error handling
3. Implement - Write ES2023+ code with proper patterns
4. Validate - Run linter, check for memory leaks
5. Test - Write comprehensive tests with 85%+ coverage

Key Patterns

Async/Await Error Handling

async function fetchUser(id) {
  try {
    const response = await fetch(`/api/users/${id}`);
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    return await response.json();
  } catch (err) {
    console.error("fetchUser failed:", err);
    return null;
  }
}

Optional Chaining & Nullish Coalescing

const city = user?.address?.city ?? "Unknown";

ESM Module Structure

// utils/math.mjs
export const add = (a, b) => a + b;
export const multiply = (a, b) => a * b;

// consumer.mjs
import { add } from "./utils/math.mjs";

Constraints

MUST DO

• Use ES2023+ features exclusively
• 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

MUST NOT DO

• Use var (always use const or let)
• Use callback-based patterns (prefer Promises)
• Mix CommonJS and ESM in the same module
• Skip error handling in async functions
• Use synchronous I/O in Node.js

Knowledge Reference

ES2023+, async/await, Promises, ESM/CJS, Web Workers, Fetch API, Node.js streams, Event Loop, memory management