ES 6/7 新特性： Promise async await

题目：一秒后打印 1，隔两秒打印 2, 再隔三秒打印 3

首先，用普通的 setTimeout 来完成：

setTimeout(() => {
    
    
    console.log(1)
    setTimeout(() => {
    
    
        console.log(2)
        setTimeout(() => {
    
    
            console.log(3)
        }, 3000)
    }, 2000)
}, 1000)

这样的嵌套多了会像一个千层蛋糕，不好看且不利于后期维护，所以有了 Promise 对象：

new Promise((resolve) => {
    
    
    setTimeout(() => {
    
    
        console.log(1)
        resolve();
    }, 1000) 
}).then(() => {
    
    
    console.log("1 done");
    return new Promise((resolve) => {
    
    
        setTimeout(() => {
    
    
            console.log(2);
            resolve();
        }, 2000)        
    })
}).then(() => {
    
    
    console.log("2 done");
    return new Promise((resolve) => {
    
    
        setTimeout(() => {
    
    
            console.log(3);
            resolve();
        }, 3000)        
    })
}).then(() => {
    
    
    console.log("3 done");
})

那么有没有更舒服的写法呢？
ES7 新增了 async await 语句：

const pp1 = () => {
    
    
    return new Promise((resolve) => {
    
    
        setTimeout(() => {
    
    
            console.log(1);
            resolve();
        }, 1000)
    })
}

const pp2 = () => {
    
    
    return new Promise((resolve) => {
    
    
        setTimeout(() => {
    
    
            console.log(2);
            resolve();
        }, 2000)
    })
}

const pp3 = () => {
    
    
    return new Promise((resolve) => {
    
    
        setTimeout(() => {
    
    
            console.log(3);
            resolve();
        }, 3000)
    })
}

const noSameTime = async () => {
    
    
    await pp1();
    await pp2();
    await pp3();
}

noSameTime();