为什么我的async/await函数异常？(Javascript)

Question

这是我的Javascript编码.我认为结果是1 2 3 4 5.

async function fn1 () {
    console.log(1);
    await fn2();
    console.log(3);
};

async function fn2 () {
    console.log(2);
};

fn1();
new Promise((resolve, reject) => {
    console.log(4)
    resolve()
}).then(() => {
    console.log(5)
})

但.结果是:1 2 4 5 3.

Answer 1

// functions declaration

async function fn1 () {
    console.log(1);
    await fn2(); // wait for async function fn2(which gets dispatched on thread 3) => so console.log(2) should be here chronologically
    console.log(3);
};

async function fn2 () {
    console.log(2);
};


// thread 1 starts (the actual execution code)

fn1(); // since fn1 is async it gets dispatched on thread 2

new Promise((resolve, reject) => {
    console.log(4)
    resolve() // trigger () => {console.log(5)}
}) // promise declaration
.then(() => {
    console.log(5)
}) // execute the promise right away

简单来说,如果console.log(1),console.log(2),console.log(3)发生在一个线程按时间顺序,console.log(4),console.log(5)发生在其他线程上按时间顺序.它们相互交叉.

附注: JavaScript本身是单线程的,不支持多线程!(除了web worker等,在我们的"async"上下文中)我简化了很多并在thread这里使用这个术语只是为了让它易于理解.为了不误解您的异步操作概念,如果您不确定异步操作如何在JavaScript中,我建议您阅读此QnA.