json2.js: This file creates a JSON property in the global object, if there
isn't already one, setting its value to an object containing a stringify
method and a parse method. The parse method uses the eval method to do the
parsing, guarding it with several regular expressions to defend against
accidental code execution hazards. On current browsers, this file does nothing,
prefering the built-in JSON object.

json.js: This file does everything that json2.js does. It also adds a
toJSONString method and a parseJSON method to Object.prototype. Use of this
file is not recommended.

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json2.js：此文件中的全局对象创建一个JSON属性，如果有
尚未之一，其值设置为一个对象，它包含一个字符串化
方法和分析方法。解析方法使用Eval方法做
解析，守着这几个正则表达式来抵御
偶然的代码执行的危险。在当前的浏览器，这个文件不执行任何操作，
喜欢内置的JSON对象。

json.js：这一切json2.js文件不一样。它还增加了一个
toJSONString方法和parseJSON方法到Object.prototype。使用本
文件不建议。