src/v8/test/mjsunit/es8/async-await-interleaved.js

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// Check for correct interleaving of Promises and async/await
(function () {
  const iterations = 10;
  let promiseCounter = iterations;
  let awaitCounter = 0;

  async function check(v) {
    awaitCounter = v;
    // The following checks ensure that "await" takes 3 ticks on the
    // microtask queue. Note: this will change in the future
    if (awaitCounter === 0) {
      assertEquals(iterations, promiseCounter);
    } else if (awaitCounter <= Math.floor(iterations / 3)) {
      assertEquals(iterations - awaitCounter * 3, promiseCounter);
    } else {
      assertEquals(0, promiseCounter);
    }
  }

  async function f() {
    for (let i = 0; i < iterations; i++) {
      await check(i);
    }
    return 0;
  }

  function countdown(v) {
    promiseCounter = v;
    if (v > 0) Promise.resolve(v - 1).then(countdown);
  }

  countdown(iterations);
  f();
})();