等待异步执行，然后再继续for循环

function asyncTask(callback) {
  setTimeout(function() {
    console.log("异步任务完成");
    callback();
  }, 1000);
}

for (var i = 0; i < 5; i++) {
  console.log("循环开始");
  asyncTask(function() {
    console.log("回调函数执行");
  });
  console.log("循环结束");
}

function asyncTask() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log("异步任务完成");
      resolve();
    }, 1000);
  });
}

for (var i = 0; i < 5; i++) {
  console.log("循环开始");
  asyncTask().then(function() {
    console.log("Promise执行");
  });
  console.log("循环结束");
}

function delay(ms) {
  return new Promise(function(resolve) {
    setTimeout(resolve, ms);
  });
}

async function asyncTask() {
  await delay(1000);
  console.log("异步任务完成");
}

async function main() {
  for (var i = 0; i < 5; i++) {
    console.log("循环开始");
    await asyncTask();
    console.log("循环结束");
  }
}

main();