JavaScript 对象操作在唯一操作后显示不同键的相同值

Question

我正在开发一个 Node.js 后端，它为相同的日期键提取不同的值。我有下面的代码，在其中我声明了一个 Month 对象，用于存储默认的日期列表(为简单起见缩短)。

然后将这些值分配给不同的键，作为要返回的最终数据对象的模板。

我通过将 numIncrease 值增加 1 来模拟数据操作。所需的输出是:

{ '2019-01-01': 6 }
{ '2019-01-01': 7 }
{ '2019-01-01': 8 }
{ '2019-01-01': 9 }

但是当我运行它时，我得到以下代码:

data: { key1: { '2019-01-01': 15 },
  key2: { '2019-01-01': 15 },
  key3: { '2019-01-01': 15 },
  key4: { '2019-01-01': 15 } }

此外，numIncrease 每次不会只增加 1。除非我错过了一个明显的范围错误，否则我听说 JavaScript 的工作方式有一些“奇怪”的东西。我仍在学习，所以这是一次很好的学习经历。

下面的示例已准备好运行。感谢您的帮助!

let months = {
    '2019-01-01': 5,
}

// key data key is assigned to months for template use
let data = {
    key1: months,
    key2: months,
    key3: months,
    key4: months,
}

// Initial Num Increase
let numIncrease = 1

/**
 * Key 1
 */
for (let date in data.key1) {
    data.key1[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key1) // key1: { '2019-01-01': 6 }

/**
 * Key 2
 */
for (let date in data.key2) {
    data.key2[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key2) // key2: { '2019-01-01': 7 }

/**
 * Key 3
 */
for (let date in data.key3) {
    data.key3[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key3) // key1: { '2019-01-01': 8 }

/**
 * Key 4
 */
for (let date in data.key4) {
    data.key4[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key4) // key4: { '2019-01-01': 9 }

// For some reason all data key nums now equal the last iteration through where key4 = 15
console.log("data: ", data)

Answer 1

在您的代码中，内存中只有一个 months 对象。所有键(key1、key2、key3 和 key4)都指向本月对象。因此，当您浏览代码时，您正在操作内存中的同一个月份对象。换句话说，它们必须相同，因为只有一个months对象!

如果您希望它们是不同的对象，请考虑在分配给所有键时创建一个副本。以下示例使用扩展运算符来执行此操作。

let months = {
    '2019-01-01': 5,
}

// key data key is assigned to months for template use
let data = {
    key1: { ...months },
    key2: { ...months },
    key3: { ...months },
    key4: { ...months }
}

// Initial Num Increase
let numIncrease = 1

/**
 * Key 1
 */
for (let date in data.key1) {
    data.key1[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key1) // key1: { '2019-01-01': 6 }

/**
 * Key 2
 */
for (let date in data.key2) {
    data.key2[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key2) // key2: { '2019-01-01': 7 }

/**
 * Key 3
 */
for (let date in data.key3) {
    data.key3[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key3) // key1: { '2019-01-01': 8 }

/**
 * Key 4
 */
for (let date in data.key4) {
    data.key4[date] += numIncrease
}
numIncrease += 1; // increase num to simulate different manipulation on next key
console.log(data.key4) // key4: { '2019-01-01': 9 }

// For some reason all data key nums now equal the last iteration through where key4 = 15
console.log(data)