请向我解释这个代码！ （JavaScript）的 [英] Please explain this code to me! (Javascript)

问题描述

我有一个名为chatRoom的变量，定义如下：

I've a variable by the name "chatRoom", defined as follows:

var chatRoom = {
	'all' : []
};

这里，我假设聊天室是一个JSON对象/数组。



现在，这里是另一段代码

Here, I assume chatroom is a JSON object/array.

Now, here is another piece of code

if (chatRoom[to]) {
		chatRoom[to].push(newChatEl);
	} else
		chatRoom[to] = [ newChatEl ];

这里，to包含一些字符串值。





我是编程新手，对Java有一点了解，但对JavaScript几乎一无所知。我在Java中学到的是，我们必须在if关键字后面的括号中放置一个布尔值。但在JavaScript中，chatroom [to]看起来不像布尔值true / false。



1.您如何在这里解释chatRoom [Harry]这个词？字符串Harry是否存储在JSON对象chatRoom中作为chatRoom = {'all'：[Harry]}？如果我们要引用Harry，我们该怎么做：chatRoom.all [0]或chatRoom [0]？



2.你是什么意思chatRoom [哈里] .push（newChatEl）？这里chatRoom不是一个数组，而是一个JSON对象。我们在chatRoom中添加一个包含newChatEl的新节点吗？作为参考，newChatEl是一堆Html代码（创建了一些 div 和 span 元素，并将它们的引用传递给newChatEl）。因此，newChatEl甚至不是String对象。如果newChatEl不是String，怎么可以推送到chatRoom [Harry]？





3.在 else 部分代码，我们创建一个数组并将newChatEl作为其第一个元素传递给它吗？



对不起，如果问题很愚蠢，但我需要完全理解它。

谢谢！



我的尝试：



需要一些解释，已在问题中解释过。

Here, "to" holds some string value.


I'm new to programming and have a little knowledge of Java but near to none knowledge of JavaScript. What I've learned in Java is that, we have to a put a statement which results in a Boolean value in the parenthesis after "if" keyword. But here in JavaScript "chatroom[to]" does not look like a Boolean true/false.

1. How would you interpret term "chatRoom[Harry]" here? Is the string "Harry" stored in the JSON object chatRoom as chatRoom={'all':[Harry]}? If we have to refer to Harry, how do we do it: chatRoom.all[0] or chatRoom[0]?

2. What do you mean by chatRoom[Harry].push(newChatEl)? Here chatRoom is not an array, but a JSON object. Are we adding a new node in Harry in chatRoom which contains newChatEl? For reference, newChatEl is a bunch of Html codes (Some div and span elements are created and their reference is passed to newChatEl). So, newChatEl is not even a String object. And if "newChatEl"is not String, how can it be pushed to chatRoom[Harry]?


3. In the else part of the code, are we creating an array and passing newChatEl in it as its first element?

Sorry, if the questions are silly, but I need to understand it completely.
Thank you!

What I have tried:

Need some explanation, already explained in the question.

推荐答案

Quote：

var chatRoom = {
    'all' : []
};

首先，尽管有些人可能会告诉你， JSON [ ^ ]仅引用包含序列化对象或数组的字符串。你有什么对象文字。



语法和类型 - JavaScript | MDN [ ^ ]



这将声明一个名为 chatRoom 的新变量，其中包含一个具有单个属性的对象叫全部。该属性包含一个空数组。





现在，在Javascript中，有两种方法可以访问对象的属性。您可以使用标准点符号：

Firstly, despite what some people might tell you, JSON[^] only ever refers to a string containing a serialized object or array. What you have there is an object literal.

Grammar and types - JavaScript | MDN[^]

This declares a new variable called chatRoom, which contains an object with a single property called all. That property contains an empty array.


Now, in Javascript, there are two ways you can access a property of an object. You can use the standard dot-notation:

var foo = chatRoom.all;

或者您可以使用括号符号：

Or you can use bracket notation:

var bar = chatRoom['all'];

第二个选项如果你没有特别有用在编写代码时不知道属性的名称：

The second option is particularly useful if you don't know the name of the property when you write the code:

var to = 'all';
var baz = chatRoom[to];

使用对象 - JavaScript | MDN [ ^ ]





Javascript更古怪的一个领域是truthy和falsey值的概念。基本上，几乎所有东西都可以被视为 bool ，并且有一些标准规则来确定它是真还是假。

Truthy and Falsy：当JavaScript中的所有内容不相同时 - SitePoint [ ^ ]



值不存在的属性 undefined 。根据规则，该值为falsey，因此：

Working with objects - JavaScript | MDN[^]


One of the more quirky areas of Javascript is the concept of "truthy" and "falsey" values. Basically, almost everything can be treated as if it were a bool, with some standard rules to determine whether it's "true" or "false".
Truthy and Falsy: When All is Not Equal in JavaScript — SitePoint[^]

The value of a property that doesn't exist is undefined. According to the rules, that value is "falsey", so:

if (chatRoom[to]) {

将执行 if 如果属性存在则阻止，如果不存在则阻止 else 阻止。





现在，您可以看到您的代码阻止：

will execute the if block if the property exists, and the else block if it doesn't.


So now, you can see that your code block:

if (chatRoom[to]) {
    chatRoom[to].push(newChatEl);
} else {
    chatRoom[to] = [ newChatEl ];
}

确定 chatRoom 是否包含具有指定名称的属性。如果是，则将 newChatEl 添加到该属性。如果没有，它会创建属性并使用包含 newChatEl 的新数组对其进行初始化。





1）除非变量到包含字符串'all'，否则此代码不会触摸所有数组。



2） chatRoom [x] .push（y ）将值 y 添加到存储在 x 中命名的属性中的数组中。属性值是数组，而不是 chatRoom 。



3）是， [ x] 是数组文字的语法 [ ^ ]包含单个值。

determines whether the chatRoom contains a property with the specified name. If it does, it adds the newChatEl to that property. If it doesn't, it creates the property and initializes it with a new array containing newChatEl.


1) Unless the variable to contains the string 'all', this code will not touch the all array.

2) chatRoom[x].push(y) adds the value y to the array stored in the property named in x. The property value is the array, not chatRoom.

3) Yes, [x] is the syntax for an array literal[^] containing a single value.

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