JavaScript中的嵌套函數返回值

我會說我是一個初學者轉換到中級程序員，我不完全理解閉包以及帶返回值的嵌套函數。我已經做了一些閱讀，不能真正包裹我的頭。JavaScript中的嵌套函數返回值

下面的代碼將只返回undefined。我會假設這是因爲它是一個嵌套函數，但我不確定如何解決它。

var Twit = require('twit'); 
 
var request = require('request'); 
 

 
var T = new Twit({ 
 
    consumer_key:   'Removed for security reasons', 
 
    consumer_secret:  'Removed for security reasons', 
 
    access_token:   'Removed for security reasons', 
 
    access_token_secret: 'Removed for security reasons', 
 
}); 
 

 
var stream = T.stream('statuses/filter', {track: '#instagram'}); 
 

 
stream.on('tweet', function(tweet){ 
 
    if(!tweet.entities.media){ 
 
    console.log("No photo here"); 
 
    }else{ 
 
    var imageUrl = JSON.stringify(tweet.entities.media[0].media_url).replace(/^"(.*)"$/, '$1'); 
 
    console.log(describeImage(imageUrl) + " - " + imageUrl); 
 
    } 
 
}); 
 

 

 
function describeImage(imageUrl){ 
 
    
 
var options = { 
 
    url: "https://api.projectoxford.ai/vision/v1.0/describe?maxCandidates=1", 
 
    json: {url: imageUrl}, 
 
    method: 'POST', 
 
    headers: { 
 
     'Content-type' : 'application/json', 
 
     'Ocp-Apim-Subscription-Key' : 'Removed for security reasons' 
 
    } 
 
} 
 

 
    request(options, function(err, res, body){ 
 
    if(err){ 
 
     console.log(err); 
 
    } 
 
    //This is where I'm going wrong. 
 
    return JSON.stringify(body.description.captions[0].text); 
 
    }); 
 
    
 
    
 
}

任何幫助將是美好的！

來源

2016-05-15 Josh Stewart-Van Dusen

'request'是異步的製作'describeImage'異步但您嘗試同步使用它。看看承諾（藍鳥）或回調。 – Wainage

做出如下修改代碼1），其中describeImage調用，並且2）其中，u是走錯了

var Twit = require('twit'); 
 
var request = require('request'); 
 

 
var T = new Twit({ 
 
    consumer_key:   'Removed for security reasons', 
 
    consumer_secret:  'Removed for security reasons', 
 
    access_token:   'Removed for security reasons', 
 
    access_token_secret: 'Removed for security reasons', 
 
}); 
 

 
var stream = T.stream('statuses/filter', {track: '#instagram'}); 
 

 
stream.on('tweet', function(tweet){ 
 
    if(!tweet.entities.media){ 
 
    console.log("No photo here"); 
 
    }else{ 
 
    var imageUrl = JSON.stringify(tweet.entities.media[0].media_url).replace(/^"(.*)"$/, '$1'); 
 
    describeImage(imageUrl,function(imgUrl){ 
 
     console.log(imgUrl + " - " + imageUrl); 
 
    }); 
 
    } 
 
}); 
 

 

 
function describeImage(imageUrl,callBack){ 
 
    
 
var options = { 
 
    url: "https://api.projectoxford.ai/vision/v1.0/describe?maxCandidates=1", 
 
    json: {url: imageUrl}, 
 
    method: 'POST', 
 
    headers: { 
 
     'Content-type' : 'application/json', 
 
     'Ocp-Apim-Subscription-Key' : 'Removed for security reasons' 
 
    } 
 
} 
 

 
    request(options, function(err, res, body){ 
 
    if(err){ 
 
     console.log(err); 
 
    } 
 
    //Call Callback function here 
 
    return callBack(JSON.stringify(body.description.captions[0].text)); 
 
    }); 
 
    
 
    
 
}

來源

2016-05-15 16:59:24

JavaScript中的嵌套函數返回值

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