复杂_异步队列问题

Question

修改下面的 start 函数, 使 execute 对应的 id 按顺序打印.

function start(id) {
  execute(id).catch(console.error);
}

/**
 * 以下为测试代码，请勿修改：
 */
console.log('输出结果:');

for (let i = 0; i < 5; i++) {
  start(i);
}

function sleep(duration) {
  return new Promise(resolve => setTimeout(resolve, duration));
}

function execute(id) {
  let duration = Math.floor(Math.random() * 500);

  return sleep(duration).then(() => {
    console.log('id', id);
  });
}

// 输出结果参考
// id 0
// id 1
// id 2
// id 3
// id 4

Answer

const waittingQueue = [];
let curTask = null;
function start(id) {
  if (curTask !== null) {
    waittingQueue.push(id);
    return;
  }
  curTask = id;
  execute(id)
    .catch(console.error)
    .then(() => {
      curTask = null;
      if (waittingQueue.length) {
        start(waittingQueue.shift());
      }
    });
}