javascript - ES2018 Async Generator 的简明部分应用？

Question

我定义了一个异步生成器函数，想创建第二个异步生成器函数，它是第一个函数的部分应用。例如，这有效:

async function* fn1(a, b) {/* do something */}

async function* fn2() {
  const a1 = fn1(0, 0);
  for await (const value of a1) {
    yield value;
  }
}

我的问题是:是否有更简洁的方法来定义fn2？

Answer 1

fn1 返回 fn2 正在迭代的异步可迭代对象，因此无需在 fn2 中手动迭代，您可以直接生成可迭代对象来自 fn1 并让 fn2 的消费者处理它:

async function* fn2() {
  yield* fn1(0, 0);
}

const delay = ms => new Promise(res => setTimeout(res, ms));
async function* fn1(a, b) {
  for (let i = 0; i < 3; i++) {
    await delay(1000);
    yield i;
  }
}

async function* fn2() {
  yield* fn1(0, 0);
}

(async () => {
  for await (const val of fn2()) {
    console.log('Consumer got', val);
  }
  console.log('Done');
})();

// Original version, without yield* (just to illustrate equivalence):

const delay = ms => new Promise(res => setTimeout(res, ms));
async function* fn1(a, b) {
  for (let i = 0; i < 3; i++) {
    await delay(1000);
    yield i;
  }
}

async function* fn2() {
  const a1 = fn1(0, 0);
  for await (const value of a1) {
    yield value;
  }
}

(async () => {
  for await (const val of fn2()) {
    console.log('Consumer got', val);
  }
  console.log('Done');
})();