javascript - JSON和对象文字表示法有什么区别？(What is the difference between JSON and Object Literal Notation?)

Question

Can someone tell me what is the main difference between a JavaScript object defined by using Object Literal Notation and JSON object ?(有人可以告诉我使用对象文字表示法定义的JavaScript对象和JSON对象之间的主要区别是什么吗？)

According to a JavaScript book it says this is an object defined by using Object Notation :(根据一本JavaScript书，它说这是使用Object Notation定义的对象 ：)

var anObject = {
    property1 : true,
    showMessage : function (msg) { alert(msg) }
};

Why isn't it a JSON object in this case?(为什么在这种情况下不是JSON对象？)

Just because it is not defined by using quotation marks?(只是因为它不是通过使用引号定义的？)   ask by pencilCake translate from so

Answer 1

Lets clarify first what JSON actually is.(首先让我们澄清一下什么是JSON 。)

JSON is a textual , language-indepedent data-exchange format, much like XML, CSV or YAML.(JSON是一种文本形式的，不依赖语言的数据交换格式，非常类似于XML，CSV或YAML。)

Data can be stored in many ways, but if it should be stored in a text file and be readable by a computer, it needs to follow some structure.(数据可以通过多种方式存储，但是如果应该将其存储在文本文件中并且可由计算机读取，则它需要遵循某种结构。)

JSON is one of the many formats that define such a structure.(JSON是定义这种结构的多种格式之一。)

Such formats are typically language-independent, meaning they can be processed by Java, Python, JavaScript, PHP, you name it.(这样的格式通常与语言无关，这意味着它们可以通过Java，Python，JavaScript，PHP进行处理，只要您命名即可。)

In contrast, JavaScript is a programming language.(相反， JavaScript是一种编程语言。)

Of course JavaScript also provides a way to define/describe data, but the syntax is very specific to JavaScript.(当然，JavaScript还提供了一种定义/描述数据的方法，但是语法非常特定于JavaScript。)

As a counter example, Python has the concept of tuples , their syntax is (x, y) .(作为反例，Python具有元组的概念，其语法为(x, y) 。)

JavaScript doesn't have something like this.(JavaScript没有这样的东西。)

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Lets look at the syntactical differences between JSON and JavaScript object literals.(让我们看一下JSON和JavaScript对象文字之间的语法差异。)

JSON has the following syntactical constraints:(JSON具有以下语法约束：)

• Object keys must be strings (ie a character sequence enclosed in double quotes " ).(对象键必须是字符串 （即用双引号"括起来的字符序列）。)
• The values can be either:(值可以是：)
  • a string(一个字符串)
  • a number(一个号码)
  • an (JSON) object(（JSON）对象)
  • an array(数组)
  • true
  • false
  • null
• Duplicate keys ( {"foo":"bar","foo":"baz"} ) produce undefined, implementation-specific results;(重复键（ {"foo":"bar","foo":"baz"} ）产生未定义的，特定于实现的结果；) the JSON specification specifically does not define their semantics(JSON规范没有明确定义其语义)

In JavaScript, object literals can have(在JavaScript中，对象文字可以具有)

• String literals, number literals or identifier names as keys (since ES6, keys can now also be computed, which introduces yet another syntax).(字符串文字，数字文字或标识符名称作为键（自ES6开始，现在还可以计算键，这引入了另一种语法）。)
• The values can be any valid JavaScript expression, including function definitions and undefined .(值可以是任何有效的JavaScript表达式，包括函数定义和undefined 。)
• Duplicate keys produce defined, specified results (in loose mode, the latter definition replaces the former; in strict mode, it's an error).(重复的键会产生已定义的指定结果（在宽松模式下，后一个定义将替换前一个；在严格模式下，这是一个错误）。)

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Knowing that, just be looking at the syntax , your example is not JSON because of two reasons:(知道了，仅查看语法 ，您的示例就不是JSON，原因有两个：)

1. Your keys are not strings (literals).(您的密钥不是字符串（文字）。) They are identifier names .(它们是标识符名称 。)
2. You cannot assign a function as a value to a "JSON object" (because JSON doesn't define any syntax for functions).(您不能将函数作为值分配给“ JSON对象”（因为JSON没有为函数定义任何语法）。)

But most importantly, to repeat my explanation from the beginning: You are in a JavaScript context.(但最重要的是，从头开始重复我的解释：您处于JavaScript上下文中。)

You define a JavaScript object.(您定义一个JavaScript对象。) If any, a "JSON object" can only be contained in a string:(如果有的话，“ JSON对象”只能包含在字符串中：)

 var obj = {foo: 42}; // creates a JavaScript object (this is *not* JSON)
 var json = '{"foo": 452}'; // creates a string containing JSON

That is, if you're writing JavaScript source code, and not dealing with a string , you're not dealing with JSON.(也就是说，如果您正在编写JavaScript源代码，并且没有处理字符串 ，那么您就不会处理JSON。)

Maybe you received the data as JSON (eg, via ajax or reading from a file), but once you or a library you're using has parsed it, it's not JSON anymore.(也许您以JSON形式接收了数据（例如，通过ajax或从文件中读取），但是一旦您或所使用的库将其解析后，它便不再是JSON。)

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Only because object literals and JSON look similar , it does not mean that you can name them interchangeably.(仅因为对象文字和JSON看起来相似 ，并不意味着您可以互换命名它们。)

See also There's no such thing as a "JSON Object" .(另请参阅没有“ JSON对象”之类的东西 。)