Does node.js support yield?

Question

Is there any way to get generators into node.js?

I\'m currently faking them with callbacks, but I have to remember to check the response of the callback inside of my gen

Answer 1

Yes Node.js and JavaScript now have both synchronous iterators (as of atleast Node v6) and asynchronous iterators (as of Node v10):

An example generator/iterator with synchronous output:

// semi-pythonic like range
function* range(begin=0, end, step=1) {
  if(typeof end === "undefined") {
    end = begin;
    begin = 0;
  }
  for(let i = begin; i < end; i += step) {
    yield i;
  }
}

for(const number of range(1,30)) {
  console.log(number);
}

A similar async generator/iterator.

const timeout = (ms=1000) => new Promise((resolve, reject) => setTimeout(resolve, ms));

async function* countSeconds(begin=0, end, step=1) {
  if(typeof end === "undefined") {
    end = begin;
    begin = 0;
  }
  for(let i = begin; i < end; i += step) {
    yield i;
    await timeout(1000);
  }
}

(async () => {
  for await (const second of countSeconds(10)) {
    console.log(second);
  }
})();

There is a lot to explore here are some good links. I will probably update this answer with more information later:

• Generators
• Generator functions
• Iterable Protocol
• Iterator Protocol
• Async Generators
  • Jake Archibald's Article on Async Generators
• Async Iterators
• for await ... of