js的三種異步方法

// 存在異步問題
let fn = () => {
    let name = '張三';
    setTimeout(() => {
        return name;
    }, 1000);
}
console.log(fn()); // undefined

// 第一種 回調函數
let fnCallback = (callback) => {
    let name = '張三fnCallback';
    setTimeout(() => {
        callback(name);
    }, 1000);
}
fnCallback((data) => {
    console.log(data);
})

// 第二種 Promise
let fbPromise = new Promise((success, error) => {
    let name = '張三fbPromise';
    setTimeout(() => {
        success(name);
    }, 1000);
})
fbPromise.then((data) => {
    console.log(data);
});

// 第三種 async await
let fbAsync = async () => {
    let name = '張三fbAsync';
    return new Promise((success, error) => {
        setTimeout(() => {
            success(name);
        }, 1000);
    })
}
async function main() {
    let abc = await fbAsync();
    console.log(abc);
}
main();