第 52 题：如何使用一个 promise？以及 Promise.all？

Promise 用法

let request = new Promise((resolve, reject) => {
    // 表达式
    if (true) {
        resolve({ age: 20 });
    } else {
        reject( 请求接口失败 );
    }
});

request
    .then(res => {
        console.log( res , res); // { age: 20 }
    })
    .catch(res => {
        console.log( res2 , res); // 请求接口失败
    });

Promise.all 用法

let requestA = new Promise(resolve => {
    setTimeout(() => {
        resolve({ requestA: 20 });
    }, 1000 * 2);
});

let requestB = new Promise(resolve => {
    resolve({ requestB: 50 });
});

let requestAll = Promise.all([requestA, requestB]).then(res => {
    console.log( res , res); // [{ requestA: 20 }, { requestB: 50 }]
});