使用ES6在没有映射的情况下递增对象属性

Question

所以，我想做的是：

创建水果的对象作为键和它们出现的次数。结束对象如下所示：

fruitsObj[fruit].name
fruitsObj[fruit].count

所以对于“苹果”来说：

fruitsObj.apple.name // apple
fruitsObj.apple.count // 4

{apple: {…}, pear: {…}, banana: {…}, orange: {…}, kumquat: {…}}
apple:{name: "apple", count: NaN}
banana:{name: "banana", count: NaN}
kumquat:{name: "kumquat", count: NaN}
orange:{name: "orange", count: NaN}
pear:{name: "pear", count: NaN}
__proto__: Object

{apple: {…}, pear: {…}, banana: {…}, orange: {…}, kumquat: {…}}
apple:{name: "apple", count: 1}
banana:{name: "banana", count: 1}
kumquat:{name: "kumquat", count: 1}
orange:{name: "orange", count: 1}
pear:{name: "pear", count: 1}
__proto__: Object

// Declare an array of fruits
var fruitsArr = ['apple', 'pear', 'apple', 'banana', 'orange', 'kumquat', 'orange', 'apple', 'apple', 'orange'];

var fruitsObj = {};

// Loop through each fruit storing name and count.
fruitsArr.forEach(function(fruit, i) {
	
	// Create each named-fruit property in object as a sub-object.
	fruitsObj[fruit] = {};
	
	fruitsObj[fruit].name = fruit;
	
	// FAILS with NaN!
	fruitsObj[fruit].count = ++fruitsObj[fruit].count;
	
});

console.log(fruitsObj);

// Declare an array of fruits
var fruitsArr = ['apple', 'pear', 'apple', 'banana', 'orange', 'kumquat', 'orange', 'apple', 'apple', 'orange'];

var fruitsObj = {};

// Loop through each fruit storing name and count.
fruitsArr.forEach(function(fruit, i) {
	
	// Create each named-fruit property in object as a sub-object.
	fruitsObj[fruit] = {};
	
	fruitsObj[fruit].name = fruit;

	// if fruit count exists and is greater than zero
	if (fruitsObj[fruit].count != undefined && fruitsObj[fruit].count > 0) {
		// increment it
		fruitsObj[fruit].count++;
	} else {
		// set it to one
		fruitsObj[fruit].count = 1;
	}	
	
});

console.log(fruitsObj);

我回顾了一堆帖子和链接，这些帖子和链接让我陷入了一个兔子洞。即便如此，他们中没有一个明确地解决了我所能说出的问题。

• 这段代码中Number对象保存属性并增加数字时发生了什么？
• 如何增加JavaScript对象中的值？
• 如何在JavaScript中使用for…语法获得循环计数器/索引？
• 遍历对象数组并在每个对象中更改一个属性
• https://javascript.info/object
• http://www.mojavelinux.com/articles/javascript_hashes.html
• https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/map

1. 为什么我的计数器不递增，而是返回'nan'？
2. 有什么特殊方法可以在赋值之前将对象属性声明为数字吗？
3. 我在理解上缺少什么来使这个工作？如何增加对象计数属性？

Answer 1

为什么我的计数器不递增，而是返回'nan'？

因为在第一种情况下，您试图递增未定义的属性。排队

fruitsObj[fruit].count = ++fruitsObj[fruit].count;

fruitsobj[fruite].count未定义，因为您从未为其分配任何数字值。您在第二个代码块中更正了此问题。

// Create each named-fruit property in object as a sub-object.
    fruitsObj[fruit] = {};

// Declare an array of fruits
    var fruitsArr = ['apple', 'pear', 'apple', 'banana', 'orange', 'kumquat', 'orange', 'apple', 'apple', 'orange'];
    
    var fruitsObj = {};
    
    // Loop through each fruit storing name and count.
    fruitsArr.forEach(function(fruit, i) {
    	
    	// Create a fruit object only if it does not exist already.
        if (!fruitsObj[fruit]) {
    	   fruitsObj[fruit] = {};
        }
    	
    	fruitsObj[fruit].name = fruit;
    
    	// if fruit count exists and is greater than zero
    	if (fruitsObj[fruit].count != undefined && fruitsObj[fruit].count > 0) 
        {
    		// increment it
    		fruitsObj[fruit].count++;
    	} else {
    		// set it to one
    		fruitsObj[fruit].count = 1;
    	}	
    	
    });
    
    console.log(fruitsObj);