一个头条实例

// 今日头条面试题
async function async1() {
    console.log('async1 start')
    await async2()
    console.log('async1 end')
}
async function async2() {
    console.log('async2')
}
console.log('script start')
setTimeout(function () {
    console.log('settimeout')
})
async1()
new Promise(function (resolve) {
    console.log('promise1')
    resolve()
}).then(function () {
    console.log('promise2')
})
console.log('script end')

基础知识

事件循环(Event Loop)、宏任务(Marco Task)与微任务(Misco Task)

解题思路

三个三个队列：A: 当前执行，B: 微任务，C: 宏任务

console.log(‘script start’) => A

setTimeout => C

console.log(‘async1 start’) => A

console.log(‘async2’) => A

console.log(‘async1 end’) => B

console.log(‘promise1’) => A

console.log(‘promise2’) => B

console.log(‘script end’) => A

分别输出ABC
script start
async1 start
async2
promise1
script end
async1 end
promise2
setTimeout