问题描述

下面的代码总是返回下面的连线对象

The below code always return the below wired object

{_U":0，_V":0，_W":空，_X":空}

{"_U": 0, "_V": 0, "_W": null, "_X": null}

作为回应.

这是我的代码

    getData = () => {
        fetch('http://192.168.64.1:3000/getAll',{
            method: 'GET',
            headers: {
                Accept: 'application/json',
                'Content-Type': 'application/json'
            }
        })
        .then((response) => {
            console.log('Response:')
            console.log(response.json())
            console.info('=================================')
        })
        .catch(err => console.error(err));

    } 

    componentDidMount(){
        this.getData();
    }

我使用 node、express、Mysql 作为后端和 react-native 前端

I am using node, express, Mysql as backend and react-native frontend

我的后端代码在这里

app.get('/getAll',(req,res) => {
    console.log('getAll method Called');
    con.query('select * from dummy',(err,results,fields) => {
        if(err) throw err;
        console.log('Response');
        console.log(results);
        res.send(results);
    });
});

上面的代码在控制台中给出了正确的输出，但 fetch API 不是.

The above code gives correct output in console but fetch API is not.

我找不到我的问题的解决方案.提前致谢.

i cant find solution for the my problem. Thanks in advance.

推荐答案

这表明您在 promise 解决之前记录了它 - 当您执行以下操作时的结果:console.log(response.json())

That indicates that you are logging the promise before it resolves - the result of when you: console.log(response.json())

如何访问 promise 回调值在函数之外?

正如@Evert 在评论中正确指出的那样，这是因为 response.json() 返回了一个 promise 对象.

As @Evert rightfully pointed out in comments, this is because response.json() returns a promise object.

因此，在您调用 response.json() 后，您需要链接一个额外的 .then()，并在其中记录已解决的承诺.

So, you'll need to chain an additional .then() after you call response.json() where you log the resolved promise.

getData = () => {
    fetch('http://192.168.64.1:3000/getAll',{
        method: 'GET',
        headers: {
            Accept: 'application/json',
            'Content-Type': 'application/json'
        }
    })
    .then(response => response.json())
    .then(data => {
        console.log(data);
    })
    .catch(err => console.error(err));
} 

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