Object-Oriented JavaScript - Third Edition

Iterators and iterables

ES6 introduces a new mechanism of iterating over data. Traversing a list of data and doing something with it is a very common operation. ES6 enhances the iteration constructs. There are two primary concepts involved with this change-iterators and iterables.

Iterators

A JavaScript iterator is an object that exposes the next() method. This method returns the next item from the collection in the form of an object that has two properties-done and value. In the following example, we will return an iterator from an array by exposing the next() method:

 //Take an array and return an iterator function iter(array){ var nextId= 0; return { next: function() { if(nextId < array.length) { return {value: array[nextId++], done: false}; } ...