README.md

Iterator Pattern

The Iterator pattern is a behavioral design pattern that provides a standardized way to traverse through a collection of elements without exposing its underlying structure.

Clients can iterate using next()/hasNext() without knowing if data comes from an array, database, or tree (abstraction) and same iterator interface works across different collections (reusability). Having this pattern implemented new traversal logic (e.g., depth-first vs. breadth-first) can be added without changing the collection.

Key Concepts

Iterator interface defines methods for traversing: typically hasNext() to check if more elements exist and next() to retrieve the next element. Collection interface declares methods for getting an iterator instance. Concrete Iterator implements the traversal behavior for a specific collection type. Concrete Collection creates and returns appropriate iterator instances.

Use Cases

1. React’s .map() for rendering lists.
2. DOM traversal APIs like NodeIterator let you walk through document elements.
3. Database cursors in MongoDB and PostgreSQL implement iterators to stream large result sets.
4. Node.js's ReadableStream use iterator patterns for processing data chunks.

Further Reading

https://refactoring.guru/design-patterns/iterator

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_generators