JSON

JSON对象包含用于解析 JavaScript Object Notation (JSON) 的方法，并将值转换为 JSON。它不能被调用或者作为构造函数，除了它的两个方法属性，它本身并没有有趣的功能。

描述

JavaScript Object Notation

JSON是用于序列化对象，数组，数字，字符串，布尔值和等等的语法null。它基于JavaScript语法，但不同于它：一些JavaScript不是JSON，有些JSON不是JavaScript。另请参阅JSON：不是的JavaScript子集。

JavaScript type	JSON differences
Objects and Arrays	Property names must be double-quoted strings; trailing commas are forbidden.
Numbers	Leading zeros are prohibited( in JSON.stringify zeros will be ignored, but in JSON.parse it will throw SyntaxError a decimal point must be followed by at least one digit.
Strings	Only a limited set of characters may be escaped; certain control characters are prohibited; the Unicode line separator (U+2028) and paragraph separator (U+2029) characters are permitted; strings must be double-quoted. See the following example where JSON.parse() works fine and a SyntaxError is thrown when evaluating the code as JavaScript: var code = '"\u2028\u2029"'; JSON.parse(code // works fine eval(code // fails

完整的JSON语法如下：

JSON = null
    or true or false
    or JSONNumber
    or JSONString
    or JSONObject
    or JSONArray

JSONNumber = - PositiveNumber
          or PositiveNumber
PositiveNumber = DecimalNumber
              or DecimalNumber . Digits
              or DecimalNumber . Digits ExponentPart
              or DecimalNumber ExponentPart
DecimalNumber = 0
             or OneToNine Digits
ExponentPart = e Exponent
            or E Exponent
Exponent = Digits
        or + Digits
        or - Digits
Digits = Digit
      or Digits Digit
Digit = 0 through 9
OneToNine = 1 through 9

JSONString = ""
          or " StringCharacters "
StringCharacters = StringCharacter
                or StringCharacters StringCharacter
StringCharacter = any character
                  except " or \ or U+0000 through U+001F
               or EscapeSequence
EscapeSequence = \" or \/ or \\ or \b or \f or \n or \r or \t
              or \u HexDigit HexDigit HexDigit HexDigit
HexDigit = 0 through 9
        or A through F
        or a through f

JSONObject = { }
          or { Members }
Members = JSONString : JSON
       or Members , JSONString : JSON

JSONArray = [ ]
         or [ ArrayElements ]
ArrayElements = JSON
             or ArrayElements , JSON

无效的空格可能存在于JSONNumber（数字必须不包含空格）或JSONString（其中它被解释为字符串中的相应字符，否则将导致错误）之外的任何位置。制表符（U+0009），回车（U+000D），换行（U+0020）和空格（U+0020）字符是唯一有效的空格字符。

方法

JSON.parse()将字符串解析为JSON，可选地转换生成的值及其属性，然后返回值。JSON.stringify()返回对应于指定值的JSON字符串，可选地只包含某些属性或以用户定义的方式替换属性值。

备注

JSON对象不被旧版本浏览器支持。你可以把下面代码放到脚本的开始位置，这样就可以在那些没有原生支持 JSON 对象的浏览器（如IE6）中使用JSON对象。

以下算法是对原生JSON对象的模仿：

if (!window.JSON) {
  window.JSON = {
    parse: function(sJSON) { return eval('(' + sJSON + ')' },
    stringify: (function () {
      var toString = Object.prototype.toString;
      var hasOwnProperty = Object.prototype.hasOwnProperty;
      var isArray = Array.isArray || function (a) { return toString.call(a) === '[object Array]'; };
      var escMap = {'"': '\\"', '\\': '\\\\', '\b': '\\b', '\f': '\\f', '\n': '\\n', '\r': '\\r', '\t': '\\t'};
      var escFunc = function (m) { return escMap[m] || '\\u' + (m.charCodeAt(0) + 0x10000).toString(16).substr(1 };
      var escRE = /[\\"\u0000-\u001F\u2028\u2029]/g;
      return function stringify(value) {
        if (value == null) {
          return 'null';
        } else if (typeof value === 'number') {
          return isFinite(value) ? value.toString() : 'null';
        } else if (typeof value === 'boolean') {
          return value.toString(
        } else if (typeof value === 'object') {
          if (typeof value.toJSON === 'function') {
            return stringify(value.toJSON()
          } else if (isArray(value)) {
            var res = '[';
            for (var i = 0; i < value.length; i++)
              res += (i ? ', ' : '') + stringify(value[i]
            return res + ']';
          } else if (toString.call(value) === '[object Object]') {
            var tmp = [];
            for (var k in value) {
              // in case "hasOwnProperty" has been shadowed
              if (hasOwnProperty.call(value, k))
                tmp.push(stringify(k) + ': ' + stringify(value[k])
            }
            return '{' + tmp.join(', ') + '}';
          }
        }
        return '"' + value.toString().replace(escRE, escFunc) + '"';
      };
    })()
  };
}

众所周知，更复杂的JSON对象 polyfills 是 JSON2 和 JSON3。

规范

Specification	Status	Comment
ECMAScript 5.1 (ECMA-262)The definition of 'JSON' in that specification.	Standard	Initial definition.
ECMAScript 2015 (6th Edition, ECMA-262)The definition of 'JSON' in that specification.	Standard
ECMAScript Latest Draft (ECMA-262)The definition of 'JSON' in that specification.	Living Standard

浏览器兼容性

Feature	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic Support	(Yes)	(Yes)	3.5	8	10.5	4
parse	(Yes)	(Yes)	3.5	8	10.5	4
stringify	(Yes)	(Yes)	3.5	8	10.5	4

Feature	Android	Chrome for Android	Edge mobile	Firefox for Android	IE mobile	Opera Android	iOS Safari
Basic Support	(Yes)	(Yes)	(Yes)	1	(Yes)	(Yes)	(Yes)
parse	(Yes)	(Yes)	(Yes)	1	(Yes)	(Yes)	(Yes)
stringify	(Yes)	(Yes)	(Yes)	1	(Yes)	(Yes)	(Yes)