Question

我有一个这样的对象：

var shoppers = {
  "Bob": {favoriteApple: "Honeycrisp"},
  "Sue": {favoriteApple: "Braeburn"},
  "Derek": {favoriteApple: "Honeycrisp"}
}

我想迭代这个对象并计算有多少人喜欢每种苹果。我怎么能这样做？

在相关的说明中，为什么这会记录为undefined三次，而不是记录实际的苹果名称？

for (var person in shoppers) {
    console.log(person.favoriteApple); // undefined
}

Answer 1

您可以使用以下

使用Object.keys和forEach
创建一个空对象以存储带计数的各种项目
在内部循环中，检查项目是否已经存在于countObj中，如果是，则增加计数，否则将计数设置为1

var shoppers = {
  "Bob": {
    favoriteApple: "Honeycrisp"
  },
  "Sue": {
    favoriteApple: "Braeburn"
  },
  "Derek": {
    favoriteApple: "Honeycrisp"
  }
};

// Create empty object to store item count
var countObj = {};

// Get the array of keys in object using `Object.keys`
// Iterate over keys array using `forEach`
Object.keys(shoppers).forEach(function(key) {
  // Get the value of favoriteApple
  var favApple = shoppers[key].favoriteApple;

  // If count exists, increment it else add count as 1
  countObj[favApple] = countObj[favApple] ? countObj[favApple] + 1 : 1;
});

console.log(countObj);
document.getElementById('result').innerHTML = JSON.stringify(countObj, 0, 4);

<pre id="result"></pre>

关于第二个问题

为什么console.log(person.favoriteApple);记录为未定义三次而不是记录实际的苹果名称？

for (var person in shoppers) {
    console.log(person.favoriteApple);
}

person

for是对象shoppers的关键字。要访问密钥的实际值，请使用shoppers[person]。

<强>代码：

for (var key in shoppers) {
    // To stop showing the inherited/prototyped properties
    if (shoppers.hasOwnProperty(key)) {
        console.log(shoppers[key].favoriteApple);
    }
}

Answer 2

使用时

for (var prop in obj)

迭代此对象的键。因此，在您的情况下，person将为Bob，Sue，Derek。

您只需使用此键访问属性值：

for (var person in shoppers)
{
    console.log(shoppers[person]);
}

Answer 3

你可以保持这样的记录：

var favoriteApples = {};
for(var name in shoppers) {
  var person = shoppers[name];
  if(!favoriteApples[person.favoriteApple]) {
    favoriteApples[person.favoriteApple] = 1;
  }else{
    favoriteApples[person.favoriteApple]++;
  }
}

console.log(favoriteApples);
// prints Object {Honeycrisp: 2, Braeburn: 1}

Answer 4

var shoppers = {
  "Bob": {favoriteApple: "Honeycrisp"},
  "Sue": {favoriteApple: "Braeburn"},
  "Derek": {favoriteApple: "Honeycrisp"}
}

$.each(shoppers,function(key,val){
  console.log(key);
  $.each(val,function(k,v){
    console.log(k + "    "  + v)
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

在JavaScript中迭代分层对象

4 个答案: