자바스크립트 Tutorial By Ellie (11)

비동기의 꽃 JavaScript async 와 await 그리고 유용한 Promise APIs

// async & await
// clear style of using promise :)

// 1. async
async function fetchUser() {
    // do network request in 10 secs....
    return 'ellie';
}

const user = fetchUser();
user.then(console.log);
console.log(user);

// 2. await
// await은 async가 붙은 함수 안에서만 사용한다.

function delay(ms)  {
    return new Promise(resolve => setTimeout(resolve, ms));
}

async function getApple() {
    await delay(3000);
    return 'apple';
}

async function getBanana() {
    await delay(3000);
    return 'banana';
}

async function pickFruits() {
    const apple = await getApple();
    const banana = await getBanana();
    return `${apple} + ${banana}`;
}

pickFruits().then(console.log);


// 3. useful Promise APIs
function pickAllFruits() {
    return Promise.all([getApple(), getBanana()]).then(fruits =>
        fruits.join(' + ')    
    );
}
pickAllFruits().then(console.log);

function pickOnlyOne() {
    return Promise.race([getApple(), getBanana()]);
}

pickOnlyOne().then(console.log);