Generators and the associated Iteration Protocol are a large topic, which we will briefly cover.
The Iteration Protocol is what's behind the new for..of loop, and some other new looping constructs. These constructs can be used with anything producing an iterator. For more about both, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols.
A generator is a kind of function which can be stopped and started using the yield keyword. Generators produce an iterator whose values are whatever is given to the yield statement. For more on this, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator.
Consider this:
$ cat gen.js ...
