jaykan / generator-experiments

Exploring and learning ES2015 generators

ES2015 Generators

Getting Started

The notion of generators is a groundbreaking new feature in ES2015, one of the few that isn't trivial to implement using the old ES5 spec. Specifically, generators help you write asynchronous code without callbacks, calculate the billionth Fibonacci number without blocking the event loop, and write web servers that actually know when they're done writing the HTTP response.

The ES2015 spec defines a generator solely in terms of which properties it has. In other words, any JavaScript object can be a generator, Any JavaScript object with a next() function and a throw() function is a generator as far as co is concerned.

Generators simplify iterator-authoring using function* and yield. A function declared as function* returns a generator instance. Furthermore, generators are subtypes of iterators which include additional next and throw. These enable values to flow back into the generator, so yield is an expression form which returns a value (or throws).