JavaScript Iterator Protocol Guide

The iterator protocol defines how to produce a sequence of values. Here's how to implement and use it.

Best Practices#

Implementation:
✓ Use generators when possible
✓ Implement return() for cleanup
✓ Make iterators themselves iterable
✓ Handle edge cases gracefully

Usage:
✓ Use for...of for iteration
✓ Use spread for collecting values
✓ Compose with utility functions
✓ Lazy evaluation for large data

Performance:
✓ Prefer lazy iteration
✓ Avoid collecting infinite iterators
✓ Use take() to limit iteration
✓ Clean up resources properly

Avoid:
✗ Forgetting Symbol.iterator
✗ Mutating while iterating
✗ Infinite loops without limits
✗ Complex state in iterators

The iterator protocol enables custom iteration behavior for any object. Use Symbol.iterator to make objects iterable, generators for simple implementation, and utility functions for composition. Iterators provide lazy evaluation and clean integration with for...of, spread, and destructuring.

JavaScript Iterator Protocol Guide

Iterator Basics#

Creating Custom Iterators#

Iterator Methods#

Practical Examples#

Infinite Iterators#

Iterator Utilities#

String Iterators#

Best Practices#

Conclusion#

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