如何终止 JavaScript 中的“无限”生成器？

Question

EDIT: I edited to include more actual code it seems my 'slimmed down' example was a bit confusing.

I have a javascript array, questions of unknown length which contains objects, one for each 'question', each of which has the shape

{
  questionID: 1,
  questionText:'bla bla bla',
  end: false
}

I also have a function, getNextQuestion that takes an id and returns a screen

const getNextQuestion = id => R.find(R.propEq(['questionID'], id))(questions);

(one could of course use Array.find for the above, but I'm exploring Ramda)

I want to write a generator that will yield a particular object from this array, chosen by a passed in id , up until an object is yielded which has end === true

That is, the object with this particular id should be the last value returned from the generator. After that the generator should yield {value: undefined, done: true

I thought to write something like this

export function* questionGenerator() {
  let nextID = 1;
  let continueLoop = true;
  while (continueLoop) {
    const question = getNextQuestion(nextID);
    if (question.end) continueLoop = false;
    nextID = yield getNextQuestion(nextID);
  }
}

which would be called like this

const qGen = questionGenerator();
const id = 1;
do {
  const result = gGen.next(i++)
  console.log(result.value)
} while (!result.done)

but I'm not sure if that's the best way to write it.

Is there a better way?

Answer 1

You could return from the generator, which will simplify your code:

 while (true) {
  const screen = getNextScreen(nextID);
  nextID = yield screen;
  if (screen.end) return;   
 }

Answer 2

You need some changes in the generator to return the generator and another change in the loop for the call of the generator.

 const questions = [{ questionID: 1, questionText:'bla bla bla', end: false }, { questionID: 2, questionText:'bla bla bla', end: false }, { questionID: 3, questionText:'bla bla bla', end: false }, { questionID: 4, questionText:'bla bla bla', end: false }, { questionID: 5, questionText:'bla bla bla', end: true }]; const getNextQuestion = (array => id => array.find(({ questionID }) => questionID === id))(questions); function* questionGenerator() { let nextID = 1; while (true) { const question = getNextQuestion(nextID); nextID = yield question; if (question.end) return; } } const gGen = questionGenerator(); var id = 1; while (true) { const result = gGen.next(id++); if (result.done) break; console.log(result.value); }

 .as-console-wrapper { max-height: 100%;important: top; 0; }