笔试题

最新推荐文章于 2025-03-11 17:49:27 发布

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本文详细解析了JavaScript中异步代码的执行流程，通过具体的示例代码展示了async/await函数、Promise对象以及setTimeout等API的执行时机和顺序。帮助读者深入理解JavaScript的异步编程机制。

异步笔试题

async function async1() {
  console.log("async1 start"); //2
  await async2();
  console.log("async1 end"); //6
}
async function async2() {
  console.log("async2"); //3
}
console.log("script start"); // 1
setTimeout(function () {
  console.log("setTimeout"); //8
}, 0);
async1();
new Promise(function (resolve) {
  console.log("promise1"); // 4
  resolve();
}).then(function () {
  console.log("promise2"); //7
});
console.log("script end"); //5

输出

script start

async1 start

async2

promise1

script end

async1 end

promise2

setTimeout

const promise = new Promise((resolve, reject) => {
  console.log(1);
  resolve();
  console.log(2);
});
promise.then(() => {
  console.log(3);
});
console.log(4);


//1243 promise构造函数同步执行，then方法异步执行的