Promise.all（）解析爲每個承諾提供相同的值

我正在編寫一個模塊，它具有使用Promise.all()來發送電子郵件給幾個用戶的承諾的功能。剝離下來的代碼，我能夠重現問題下面的代碼片段：Promise.all（）解析爲每個承諾提供相同的值

var getPromise = function(data) { 
    return new Promise((resolve, reject) => { 
     console.log("After Calling:\t\t", data.user); 
     setTimeout(function() { 
       console.log("While Resolving:\t", data.user); 
       return resolve(data); 
      }, 
      Math.random() * 1000); 
    }); 
} 

var getAllPromises = function(users, options) { 
    var promises = []; 
    users.forEach(user => { 
     var userSpecificOptions = options; 
     // var userSpecificOptions = {}; 
     userSpecificOptions.user = user; 
     promises.push(getPromise(userSpecificOptions)); 
    }); 
    return Promise.all(promises); 
} 

var userlist = ["help", "promises", "are", "tough"]; 
var commonoptions = { 
    str: "something", 
} 

getAllPromises(userlist, commonoptions) 
    .then(data => console.log("Data:\n", data))

這給了我下面的輸出：

After Calling:  help 
After Calling:  promises 
After Calling:  are 
After Calling:  tough 
While Resolving:  tough 
While Resolving:  tough 
While Resolving:  tough 
While Resolving:  tough 
Data: 
[ { str: 'something', user: 'tough' }, 
    { str: 'something', user: 'tough' }, 
    { str: 'something', user: 'tough' }, 
    { str: 'something', user: 'tough' } ]

然而，切換聲明userSpecificOptions：

 // var userSpecificOptions = options; 
     var userSpecificOptions = {};

得到正確結果：

After Calling:  help 
After Calling:  promises 
After Calling:  are 
After Calling:  tough 
While Resolving:  help 
While Resolving:  promises 
While Resolving:  are 
While Resolving:  tough 
Data: 
[ { user: 'help' }, 
    { user: 'promises' }, 
    { user: 'are' }, 
    { user: 'tough' } ]

可能是什麼問題？我覺得可能有些事情我對Promises的工作方式缺乏瞭解。

來源

2017-09-16 Rohitt Vashishtha

你讓所有userSpecificOptions情況下指的是同一options對象：

var userSpecificOptions = options;

所以，當你分配給userSpecificOptions.user，你居然修改options。

相反，你應該採取的options副本：

var userSpecificOptions = Object.assign({}, options);

那麼任何變動，特別userSpecificOptions對象，不會影響options或任何其他變量。

來源

2017-09-16 21:43:35 trincot

此問題不在承諾中。在JavaScript對象是通過引用傳遞。這意味着在這種情況下，你總是改變同一個對象，最後的改變發生，你會看到所有相同的結果。當創建新對象而不是修改存在對象時，它正常工作。

來源

2017-09-16 21:46:10 alexKhymenko

Promise.all（）解析爲每個承諾提供相同的值

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