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name: javascript description: Best practices for JavaScript/TypeScript development including modern ES6+ patterns, error handling, and performance optimization. globs: ["/*.js", "/.mjs", "**/.cjs", "/*.jsx", "/.ts", "**/.tsx"] priority: 100 tags: ["language"]

JavaScript/TypeScript Best Practices

Code Style

• Use const by default, let when reassignment is needed
• Use template literals for string interpolation
• Prefer arrow functions for callbacks
• Use destructuring for object/array access
• Use async/await over .then() chains
• Use semicolons consistently (pick a style)

Error Handling

• Always handle promise rejections with .catch() or try/catch
• Use try/catch with async/await
• Provide meaningful error messages with context
• Don't swallow errors silently
• Create custom error classes for domain errors

Modern Patterns

• Use optional chaining (?.) and nullish coalescing (??)
• Use spread operator for shallow object/array copies
• Use Map/Set for complex data structures
• Prefer for...of over forEach for iterables
• Use Object.entries/keys/values for object iteration
• Use Array.from() for array-like conversions

TypeScript Specific

• Prefer interfaces over type aliases for objects
• Use strict mode in tsconfig.json
• Avoid 'any' type - use 'unknown' if needed
• Use generics for reusable type-safe code
• Use discriminated unions for type narrowing
• Leverage const assertions for literal types

Performance

• Avoid creating functions inside loops
• Use object pools for frequent allocations
• Debounce/throttle expensive operations
• Use Web Workers for CPU-intensive tasks