Generators

There is no proposal for a standard generator, but for the sake of completeness, if an array iterator consumes an array, an array generator would lazily produce one. An array generator object would implement yield as a method with behavior analogous to the same keyword within a generator function. The yield method would add a value to the array.

var array = [];
var generator = generate(array);
generator.yield(10);
generator.yield(20);
generator.yield(30);
expect(array).toEqual([10, 20, 30]);

Since ECMAScript 5, at Doug Crockford’s behest, JavaScript allows keywords to be used for property names, making this parallel between keywords and methods possible. A generator might also implement return and throw methods, but a meaningful implementation for an array generator is a stretch of the imagination. Although an array generator is of dubious utility, it foreshadows the interface of asynchronous generators, for which meaningful implementations of return and throw methods are easier to obtain, and go on to inform a sensible design for asynchronous generator functions.