promise - 承诺未决

Question

我正在尝试结合 fetch API 和 Promise

当我这样做时，一切正常

queryAPI(currency, cryptocurrency){
    const url = fetch('https://api.coinmarketcap.com/v1/ticker/')
       .then(response => response.json())
       .then(data => console.log(data));

}

但是，当我尝试将其存储在变量中时，承诺一直处于未决状态

queryAPI(currency, cryptocurrency){
    const url = fetch('https://api.coinmarketcap.com/v1/ticker/')

        .then(response => {
            const user = response.json()
            console.log(user);
        });

}

1）我做错了什么？

2）有什么方法可以在函数之外获取“用户”的值？

谢谢

标签： promise

Answer 1

该.json方法还返回一个承诺。您必须.then再次调用才能获得最终结果：

queryAPI(currency, cryptocurrency){
    const url = fetch('https://api.coinmarketcap.com/v1/ticker/')
        .then(response => response.json())
        .then(user => console.log(user))

}

因此您可以从该方法返回链式.thensqueryAPI并在其余代码中使用它：

const queryAPI = (currency, cryptocurrency) => {
    return new Promise((resolve, rej) => {
        return fetch('https://api.coinmarketcap.com/v1/ticker/')
            .then(response => response.json())
            .then(data => resolve({user: data, currency: 'EUR'}))
            .catch(e => rej(e))
    });
};

queryAPI('EU', 'bitcoin').then(data => {
   console.log(data.user);
   console.log(data.currency)
});