题目3

let res = function () {
    console.log(1);
    return new Promise((resolve, reject) => {
        console.log(2);
        resolve(4);
    })
}
new Promise(async (resolve, reject) => {
    console.log(3);
    let test = await res();
    console.log(test);
})
console.log(5);
new Promise((resolve, reject) => {
    console.log(6);
});
console.log(7);

分析

time 2m

let res = function () {
    console.log(1);
    return new Promise((resolve, reject) => {
        console.log(2);
        resolve(4);
    })
}
new Promise(async (resolve, reject) => {
    console.log(3);
    //promise1
    let test = await res();
    /**
     * await res()
     *相当于res()运行，之后then
     * res().then((res)=>{
     *     console.log(test);
     * })
     */
    console.log(test);
})
console.log(5);
new Promise((resolve, reject) => {
    console.log(6);
});
console.log(7);

async function test(){
}
console.log(test())

test()运行返回promise

async function test(){}相当于new Promise（）

await test()相相当于test().then，test()返回promise，相当于promise.then()，类似于下面代码

   let test = await res();
    /**
     * await res()
     *相当于res()运行，之后then
     * res().then((res)=>{
     *     console.log(test);
     * })
     */

可以分析成、等价于以下代码

;(function () {
    console.log(1);
    return new Promise((resolve, reject) => {
        console.log(2);
        resolve(4);
    })
})().then();
  new Promise((resolve, reject) => {
        console.log(2);
        resolve(4);
   }).then()

执行栈
script
function ->res 这只是res赋值为函数，但没有运行
3 new promise回调函数虽然是async，但是里面是同步代码，await有区别
1 运行res（），打印1
2
5
6
7
promise1.then cb ->4

宏任务

微任务
promise1
promise1.then cb x

变形1

time 8m53s

let res = function () {
    console.log(1);
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            new Promise((resolve) => {
                console.log(2);
                setTimeout(() => {
                    console.log(3)
                })
            })
        }, 0)
        resolve(5);
    })
}
new Promise(async (resolve, reject) => {
    setTimeout(() => {
        Promise.resolve().then(() => {
            console.log(4);
        })
    }, 0);
    //promise1
    let test = await res();
    /**
     * await res()
     *
     * res().then((res)=>{
     *     console.log(test);
     * })
     */
    console.log(test);
})
setTimeout(() => {
    console.log(6);
}, 0)
new Promise((resolve, reject) => {
    setTimeout(() => {
        console.log(7);
    })
}, 0);
console.log(8);

分析

先标注上setTimeout、promise，可以不标序号，分析时再标记，现在标记，省得分析时候忘记了

let res = function () {
    console.log(1);
    return new Promise((resolve, reject) => {
        //setTimeout
        setTimeout(() => {
            new Promise((resolve) => {
                console.log(2);
                //setTimeout
                setTimeout(() => {
                    console.log(3)
                })
            })
        }, 0)
        resolve(5);
    })
}
new Promise(async (resolve, reject) => {
    //setTimeout
    setTimeout(() => {
        //promise
        Promise.resolve().then(() => {
            console.log(4);
        })
    }, 0);
    //promise
    let test = await res();
    console.log(test);
})
//setTimeout
setTimeout(() => {
    console.log(6);
}, 0)
new Promise((resolve, reject) => {
    //setTimeout
    setTimeout(() => {
        console.log(7);
    })
}, 0);
console.log(8);

在setTimeout后面标注序号，省得之后忘记了

写awaitPromise与promise都可以
awaitPromise.then cb与promise.then都可以，做好加数字序号，可能太麻烦了
这道题与上面的题目意思差不多，但步骤很多，步骤多就容易犯错、失误，得精神集中

执行栈

微任务

宏任务