JSON

JSON 物件包含了解析、或是轉換為 JavaScript Object NotationJSON)格式的方法。這物件不能被呼叫或建構;而除了它的兩個方法屬性以外,本身也沒有特別的功能。

描述

JavaScript Object Notation

JSON 是序列物件、陣列、數字、字串、布林值、還有 null 的語法。它建基、但不同於 JavaScript:有些 JavaScript 不是 JSON、而有些 JSON 不是 JavaScript。請參見 JSON: The JavaScript subset that isn't

JavaScript 與 JSON 的差別
JavaScript 型別 與 JSON 的差別
物件與陣列 屬性名稱必須是包含在雙引號中的字串;禁止尾後逗號。
數字 數字不可以0作為開頭(在 JSON.stringify 0會被忽略,但是在 JSON.parse 會造成語法錯誤);小數點前面必須至少有一位數字。
字串

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

JSON 的完整語法如下:

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

Insignificant whitespace may be present anywhere except within a JSONNumber (numbers must contain no whitespace) or JSONString (where it is interpreted as the corresponding character in the string, or would cause an error). The tab character (U+0009), carriage return (U+000D), line feed (U+000A), and space (U+0020) characters are the only valid whitespace characters.

方法

JSON.parse()
解析 JSON 字串,能改變給定值和屬性、接著回傳解析值。
JSON.stringify()
回傳給定的 JSON 對應字串,可自行決定只想包括哪些特定屬性、或替換的屬性值。

Polyfill

舊版瀏覽器並不支援 JSON。你可以在程式碼開頭插入以下程式碼,以解決這個問題。這個程式碼能實做不支援原生 JSON 物件的瀏覽器(如 Internet Explorer 6)。

以下演算法能仿製原生 JSON 物件。

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) + '"';
      };
    })()
  };
}

More complex well-known polyfills for the JSON object are JSON2 and JSON3.

規範

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 (ECMA-262)
The definition of 'JSON' in that specification.
Living Standard  

瀏覽器相容性

BCD tables only load in the browser

參見