Question

在以下代码中，为什么最后一个axios.get( url.toString())不返回承诺而是返回未定义？我们该如何处理？

function getCommentersEmailIds( username ) {
    let foundUserId = undefined;
    //first get user id of username
    axios.get( 'https://jsonplaceholder.typicode.com/users?username='+username )
    .then(function( response ) {
        var foundUser = response.data.find(u=>u.username === username);
        return foundUser.id;
    })
    .then(function( userId ) {
        let url = 'https://jsonplaceholder.typicode.com/users/'+ userId.toString() +'/posts';
        return axios.get( url.toString());
    })
    .then(function( posts ) {
        //get id of the first post
        let postId = posts.data[0].id;
        let url = 'https://jsonplaceholder.typicode.com/comments?' + postId.toString();
        return axios.get(  url.toString());
    })
    .catch(function( error ) {
        console.log( error.message );
    });
}

var promiseForComments = getCommentersEmailIds('Bret');
promiseForComments.then(function( comments ) {
   comments.data.array.forEach(comment => {
       console.log(comment.email);
   }); 
})
.catch(function( error ) {
    console.log( error.message );
});

Answer 1

这里的问题是，您缺少return中的getCommentersEmailIds()语句，而不是第二个对axios.get的调用所特有的问题：

function getCommentersEmailIds( username ) {
    let foundUserId = undefined;

    //Update: add return before axio.get
    return axios.get( 'https://jsonplaceholder.typicode.com/users?username='+username )
    .then(function( response ) {
        var foundUser = response.data.find(u=>u.username === username);
        return foundUser.id;
    })
    .then(function( userId ) {
        let url = 'https://jsonplaceholder.typicode.com/users/'+ userId.toString() +'/posts';
        return axios.get( url.toString());
    })
    .then(function( posts ) {
        //get id of the first post
        let postId = posts.data[0].id;
        let url = 'https://jsonplaceholder.typicode.com/comments?' + postId.toString();
        return axios.get(  url.toString());
    })
    .catch(function( error ) {
        console.log( error.message );
    });
}

通过从axios.get()返回getCommentersEmailIds()的承诺，随后的链接（导致forEach()上的comments.data.array迭代）应按预期执行。

希望有帮助！

Answer 2

您没有从getCommentersEmailIds函数返回任何内容

做到

/usr/include/uuid/uuid.h

}

为什么axios.get不返回承诺

2 个答案: