[EcmaScript] await an async function call

async function f1() {
    let r1 = await f2();
    console.warn(r1);    //4

    return r1 + 1;
}

async function f2() {
    let r2 = await new Promise((res, rej) => {
        setTimeout(() => {
            res(1);
        }, 1000);
    });

    let r3;

    try {
        r3 = await new Promise((res, rej) => {
            setTimeout(() => {
                rej(2);
            }, 1000);
        });
    } catch (ex) {
        console.info(ex);    //2
        r3 = 3;
    }

    return r2 + r3;
}

f1().then(v => {
    console.log(v);    //5
});

주: (1) 모든 asyncfunction 성명은 실제적으로 asyncfunctionobject를 만들 것입니다. 이 object의constructor는 AsyncFunction입니다.

Object.getPrototypeOf(async function(){}).constructor
// function AsyncFunction() { [native code] }

(2)asyncfunction 호출 후promise를 되돌려줍니다. promiseresolve의 값은 async 함수 마지막return의 값입니다.
When an async function is called, it returns a Promise. When the async function returns a value, the Promise will be resolved with the returned value. When the async function throws an exception or some value, the Promise will be rejected with the thrown value.
(3)awaitpromise 표현식은promiseresolve나reject 이후에 계속 실행됩니다. 만약promisereject가 실행되면awaitpromise 표현식이 이상하게 됩니다.
An async function can contain an await expression, that pauses the execution of the async function and waits for the passed Promise's resolution, and then resumes the async function's execution and returns the resolved value.

참조:

async function - MDN Async Functions - TC39