Axios在控制台上打印值，但返回未定义 [英] Axios prints value on console but returns undefined

问题描述

一段时间以来，我遇到了一个很大的问题，这让我感到不安，这没有任何意义.我已经在我的React前端上使用了axios，当将get值分配给状态时，它可以完美地工作.但是当在普通的javascript代码中使用它时，我似乎遇到以下问题:我可以在控制台中打印对象的值，但它只会返回未定义的值.这是我的代码:

I have quite an issue for some time and is getting on my nerves and it doesn't make sense. I have used axios on my react frontend and it works perfect when assigning the get value to the state. But when using it in a normal javascript code, I appear to have this following issue: i can print the object's value in the console but it will return only undefined.. Here is my code:

login = () => {
        let data;
        axios.get('https://myaddress/authenticate')
            .then(response => {
                data = response;
                console.log('data here', data);
            })
            .catch(error => {
                console.error('auth.error', error);
            });
        console.log('eee', data);
        return data;
    };

在这里，我们严格地谈论axios.

Here we are talking about axios strictly.

推荐答案

您无法返回ajax响应，因为它是异步的.您应该将函数包装为Promise或传递回调以登录

You can't return an ajax response because it's asynchronous. You should wrap your function into a promise or pass a callback to login

更新:正如@Thilo在评论中说的那样，async/await是另一种选择，但是它可以让您将响应设置为...

UPDATE: As @Thilo said in the comments, async/await would be another option, but it will let you set the response to data tho ...

1.兑现诺言

 login = () => new Promise((resolve, reject)=>{
      axios.get('https://myaddress/authenticate')
      .then(response => {
           resolve(response)
      })
      .catch(error => {
           reject(error)
      });
 });

 // Usage example
 login()
    .then(response =>{
       console.log(response) 
    })
    .catch(error => {
       console.log(error)
    })

2.传递回叫

login = (callback) => {

   axios.get('https://myaddress/authenticate')
        .then(response => {
            callback(null,response)
        })
        .catch(error => {
            callback(error,null)
        });
};

// Usage example
login((err, response)=>{

     if( err ){
       throw err;
     }

     console.log(response);

})

3.异步/等待

login = async () => {

  // You can use 'await' only in a function marked with 'async'

  // You can set the response as value to 'data' by waiting for the promise to get resolved
  let data = await axios.get('https://myaddress/authenticate');

  // now you can use a "synchronous" data, only in the 'login' function ...
  console.log('eee', data);

  return data; // don't let this trick you, it's not the data value, it's a promise

};

// Outside usage
console.log( login() ); // this is pending promise

这篇关于Axios在控制台上打印值，但返回未定义的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！