如何在使用Promise的節點中編寫同步功能

Question

1.如何在節點中同步寫入Promises，以便獲得所需的輸出。我是一個新手，並會感謝任何幫助/建議。

// This is my core function 

var compareData = function(userIdArray) { 
    return new Promise(function(resolve, reject) { 
    var missingArray = new Array(); 
    userIdArray.forEach(function(id) { 
     var options = { 
     method: 'POST', 
     url: 'http://localhost:6006/test1', 
     headers:{ 
     'content-type': 'application/json' }, 
      body: { email: id }, 
      json: true 
     }; 

     request(options, function (error, response, body) { 
     missingArray.push(body); 
     }); 
    }); 
    resolve(missingArray); 
    }); 
} 


//I'm calling my function here 

compareData(userIdArray) 
.then(function(missingArray){ 
    console.log("The Body is: "+ missingArray); 
}); 

/* I expect the console.log to print the missingArray with data from my POST call, 
but it prints an empty array. Can someone please tell me how to do this synchronously. 
I'm pretty new to Node and finding it difficult to understand.*/ 

Answer 1

與bluebird和request-promise：

var Promise = require('bluebird'); 
var request = require('request-promise'); 

var compareData = function(userIdArray) { 
    //Promise.all(): 
     //takes an array of promises (and/or values), 
     //returns a promise of the resolved array 
    return Promise.all( 
     userIdArray.map(function(id){ 
      return request({ 
       method: 'POST', 
       url: 'http://localhost:6006/test1', 
       headers: { 'content-type': 'application/json' }, 
       body: { email: id }, 
       json: true 
      }); 
     }) 
    ); 
} 

有什麼需要進一步的解釋？

Answer 2

沒有圖書館，並假設request尚未返回一個承諾

var compareData = function(userIdArray) { 
    return Promise.all(
     userIdArray.map(function(id) { 
      var options = { 
       method : 'POST', 
       url  : 'http://localhost:6006/test1', 
       headers : { 'content-type': 'application/json' }, 
       body : { email: id }, 
       json : true 
      }; 

      return new Promise(function(resolve, reject) { 
       request(options, function(error, response, body) { 
        if (error) { 
         reject(); 
        } else { 
         resolve(body); 
        } 
       }); 
      }); 
     }) 
    ); 
} 

compareData(userIdArray).then(function(missingArray) { 
    console.log(missingArray); 
}); 

Answer 3

如果你不想使用外部庫根據@Thomas的回答，您可以直接使用原生的承諾 - 這不是太多冗長

var compareData = function compareData(userIdArray) { 
    return Promise.all(userIdArray.map(function (id) { 
     return new Promise(function (resolve, reject) { 
      var options = { 
       method: 'POST', 
       url: 'http://localhost:6006/test1', 
       headers: { 
        'content-type': 'application/json' 
       }, 
       body: { 
        email: id 
       }, 
       json: true 
      }; 
      return request(options, function (error, response, body) { 
       error ? reject(error) : resolve(body); 
      }); 
     }); 
    })); 
}; 

compareData(userIdArray) 
.then(function (missingArray) { 
    console.log("The Body is: " + missingArray); 
}); 

或者，因爲這是節點，它可以處理更多的現代代碼：

var compareData = userIdArray => 
    Promise.all(userIdArray.map(id => 
     new Promise((resolve, reject) => 
      request({ 
       method: 'POST', 
       url: 'http://localhost:6006/test1', 
       headers: { 
        'content-type': 'application/json' 
       }, 
       body: { 
        email: id 
       }, 
       json: true 
      }, (error, response, body) => error ? reject(error) : resolve(body)) 
     ) 
    )); 

compareData(userIdArray) 
.then(missingArray => 
    console.log("The Body is: "+ missingArray) 
);