You Don't Know JS: ES6 & Beyond

Chapter 3. Organization

It’s one thing to write JS code, but it’s another to properly organize it. Utilizing common patterns for organization and reuse goes a long way to improving the readability and understandability of your code. Remember: code is at least as much about communicating to other developers as it is about feeding the computer instructions.

ES6 has several important features that help significantly improve these patterns, including iterators, generators, modules, and classes.

Iterators

An iterator is a structured pattern for pulling information from a source in one-at-a-time fashion. This pattern has been found in programming for a long time. And to be sure, JS developers have been ad hoc designing and implementing iterators in JS programs since before anyone can remember, so it’s not at all a new topic.

What ES6 has done is introduce an implicit standardized interface for iterators. Many of the built-in data structures in JavaScript will now expose an iterator implementing this standard. And you can also construct your own iterators adhering to the same standard, for maximal interoperability.

Iterators are a way of organizing ordered, sequential, pull-based consumption of data.

For example, you may implement a utility that produces a new unique identifier each time it’s requested. Or you may produce an infinite series of values that rotate through a fixed list, in round-robin fashion. Or you could attach an iterator to a database query result to pull out new rows ...