蓝鸟承诺返回“未定义"当在“then"里面返回时功能 [英] BlueBird Promises returns "Undefined" when return inside "then" function

问题描述

这是我的代码:

检查用户是否关注官方 Twitter 帐户(这里我返回了新的 Promise

var isFollowing = function(sender) {
    return new promise(function(resolve, reject) {
        var following = false;
        var params = {
            source_id: sender,
            target_screen_name: config.get('twitter.official_account')
        };
        TwitObj.get('friendships/show', params, function(err, data) {
            if (!err) {
                following = data.relationship.source.following;
                resolve(following);
            } else {
                reject(err);
            }
        });
    });
};

验证:

var validateMsg = function(dm) {
    var sender = getSender(dm);
    var result = [];
    isFollowing(sender.id)
        .then(function(response) {
            if (!response) {
                result = interactiveMessage(false, lang.__('FOLLOW_MAIN', sender.name));
                console.log(result); // Displays as expected
                return result; // Not returning value Do I need to return promise again? If yes, WHY?
            }
        });
};

主要实现:

var direct_message = function(msg) {
    verifyAccount().catch(function(err) {
        console.error(err);
    });
    var dm = msg.direct_message;
    var result = validateMsg(dm);

    console.log(result);
};

问题是我应该如何强制 validateMsg 函数在 then 函数中返回 result 变量.

Questions is how should I force validateMsg function to return result variable inside then function.

更新:在调试时，我了解到，console.log(response) 在抛出 undefined 后，验证函数稍后显示then"函数，表示程序无法得到响应由于异步性质，I/O 不会立即被阻塞.如何解决这个问题?

Update: While debugging, I got to know that, console.log(response) in validation function is displaying later after throwing undefined in "then" function which means program is not able to get response immediately and due to async nature, I/O is not getting blocked. How to tackle this?

推荐答案

您实际上并未在 validateMsg 函数中返回任何内容.您在 .then 函数中返回一个同步值 ( result )，这是一个单独的函数.

You're not actually returning anything in the validateMsg function. You're returning a synchronous value ( result ) in the .then function which is a separate function.

要考虑的第二件事是您期待 validateMsg 函数，它是异步的以同步行为.

The second thing to consider is that you're expecting the validateMsg function, which is asynchronous to behave synchronously.

var 结果 = validateMsg(dm);

实现我认为您想要做的事情的方法包括进行以下更改:1)在validateMsg函数中返回promise链.

The way to achieve what I believe you're looking to do involves making the following changes: 1) Return the promise chain in the validateMsg function.

    var validateMsg = function(dm) {
    var sender = getSender(dm);
    var result = [];
    return isFollowing(sender.id)
      .then(function(response) {
          if (!response) {
              result = interactiveMessage(false, lang.__('FOLLOW_MAIN', sender.name));
              return result;
          }
        // Not sure what you want to do here if there is a response!
        // At the moment you're not doing anything if the validation
        // is successful!
        return response;
    });

};

2) 更改您的函数调用，因为您现在要返回一个 promise.

2) Change your function call, since you're now returning a promise.

    validateMsg(dm).then( function( result ){
      console.log( result );
    })

3) 如果只是为了帮助您调试，请考虑在某处添加一个 catch :)

3) Consider adding a catch somewhere if only to help you debug :)

    validateMsg(dm).then( function( result ){
      console.log( result );
    })
    .catch( function( err ){
      console.log( "Err:::", err );
    });

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