generators.js

const repeatedly = function* (x) {
  while(true) {
    yield x;
  }
}

const cycle = function* (list) {
  while(true) {
    for (x of list) {
      yield x;
    }
  }
}

const take = function(times,generator) {
  let x=generator.next();
  let result=[];
  while(!x.done && times>0) {
    result.push(x.value);
    x = generator.next();
    times--;
  }
  return result;
}

take(10,repeatedly(100));
take(20,cycle(['a','b','c']));