A closure is a function that remembers its lexical scope even when executed outside that scope. Here's how they work.
Basic Closure
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Creating Private State
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Function Factories
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Event Handlers
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Module Pattern
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Memoization
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Partial Application
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Debounce and Throttle
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Common Pitfalls
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Advanced Patterns
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Best Practices
Use Closures For:
✓ Private state and encapsulation
✓ Function factories
✓ Partial application
✓ Memoization and caching
Memory Considerations:
✓ Capture only needed variables
✓ Nullify references when done
✓ Watch for circular references
✓ Profile memory usage
Avoid:
✗ Capturing loop variables with var
✗ Excessive closure depth
✗ Capturing large objects unnecessarily
✗ Creating closures in tight loops
Conclusion
Closures are fundamental to JavaScript, enabling private state, function factories, and powerful patterns like memoization and partial application. Understand lexical scope and be mindful of memory implications. Use let/const in loops to avoid common variable capture issues.