Iterator Pattern
Intent
Provide a way to access the elements of a collection without exposing the underlying representation.
When to use
When your collection has a complex data structure under the hood, but you want to hide its complexity from clients (either for convenience or security reasons).
To support multiple traversal techniques for a collection.
You want to provide a uniform interface for traversing different types of collections (Polymorphic Iteration).
To reduce duplication of the traversal code across your app.
Structure
Iterator: defines an interface for accessing and traversing elements.
ConcreteIterator: implements the iterator interface for a certain collection.
IterableCollection: defines an interface for creating an iterator object.
ConcreteCollection: keeps track of the current object (data structure).
Notes
Most of the programming languages provide their own ways of implementing iterators. TypeScript (and JS of course) provide an interface for the Iterators, and a Symbol in the class to create the iterators so the Collection will be able to participate in for..of loops (check example 2 and 3). Also generator functions return iterators so they can be used as iterators (Check example 3).
Examples
You can find the tests here.
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