Javascript Object Addition Assignment Operator

我想在一個JavaScript對象中使用一個附加賦值運算符，以便在學生選舉中累計投票數。鑑於以下幾點：Javascript Object Addition Assignment Operator

var votes = { 
    "Alex": { president: "Bob", vicePresident: "Devin", secretary: "Gail", treasurer: "Kerry" }, 
    "Bob": { president: "Mary", vicePresident: "Hermann", secretary: "Fred", treasurer: "Ivy" }, 
    "Cindy": { president: "Cindy", vicePresident: "Hermann", secretary: "Bob", treasurer: "Bob" }, 
    "Devin": { president: "Louise", vicePresident: "John", secretary: "Bob", treasurer: "Fred" }, 
    "Ernest": { president: "Fred", vicePresident: "Hermann", secretary: "Fred", treasurer: "Ivy" }, 
    "Fred": { president: "Louise", vicePresident: "Alex", secretary: "Ivy", treasurer: "Ivy" }, 
    "Gail": { president: "Fred", vicePresident: "Alex", secretary: "Ivy", treasurer: "Bob" }, 
    "Hermann": { president: "Ivy", vicePresident: "Kerry", secretary: "Fred", treasurer: "Ivy" }, 
    "Ivy": { president: "Louise", vicePresident: "Hermann", secretary: "Fred", treasurer: "Gail" }, 
    "John": { president: "Louise", vicePresident: "Hermann", secretary: "Fred", treasurer: "Kerry" }, 
    "Kerry": { president: "Fred", vicePresident: "Mary", secretary: "Fred", treasurer: "Ivy" } 
};

我試圖瓶坯的/在以計數和創建候選人姓名的新對象和投票數圈，他們有：

var President = {}; 
for (var student in votes) { 
    President[votes[student].president] += 1; 
};

你可能已經知道，這給了我所有的NaN值。

如何獲得每次迭代增加財產的密鑰？

來源

2015-04-23 Kyle Snow Schwartz

'President'是一個空對象，增量爲null，你得到NaN，你需要給它一些初始數值。 –

問題是你沒有初始化值。所以，你會遇到一個名稱的第一次，你有President[votes[student].president]爲未定義，所以undefined + 1會給你NaN，此後每增加會給你NaN因爲NaN + 1是NaN

var President = {}, president; 
for (var student in votes) { 
    president = votes[student].president; 
    if (!President[president]) { 
     President[president] = 0; 
    } 
    President[president] += 1; 
};

來源

2015-04-23 01:07:37

你只需要在增加它之前用一個值初始化President[votes[student].president]。也許有這樣的事情：

if(President[votes[student].president]) { 
    President[votes[student].president] += 1 
} else { 
    President[votes[student].president] = 1; 
}

來源

2015-04-23 01:05:52

更改您的代碼爲這一個，你看你需要初始化你的變量;）

var President = {}; 
    for (var student in votes) { 
     if(!President[votes[student].president]){ 
     President[votes[student].president] = 0; 
     } 
     President[votes[student].president] += 1; 
    };

來源

2015-04-23 01:08:00

Javascript Object Addition Assignment Operator

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