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 }]
});

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