Iterators and Generators

In their simplest forms, iterators and generators are two ways to process a collection of data incrementally. They gain efficiency over loops by keeping track of the state of the collection instead of all of the items in the collection.

Iterators

An iterator is a way to traverse through data in a collection. To iterate over a data structure means to step through each of its elements in order. For example, the for/in loop is a method that's used to iterate over the keys in a JavaScript object. An object is an iterator when it knows how to access its items from a collection one at a time, while tracking position and finality. An iterator can be used to traverse custom complicated data structure or for traversing chunks of large data that may not be practical to load all at once.

To create an iterator, we must define a function that takes a collection in as the parameter and returns an object. The return object must have a function property called...