JSON
The JSON
object contains methods
for parsing JavaScript Object
Notation (JSON) and converting values to JSON. It can't be
called or constructed, and aside from its two method properties, it has no interesting
functionality of its own.
Description
JavaScript and JSON differences
JSON is a syntax for serializing objects, arrays, numbers, strings, booleans, and
null
. It is based upon JavaScript syntax but is distinct from it: some
JavaScript is not JSON.
- Objects and Arrays
- Property names must be double-quoted strings; trailing commas are forbidden.
- Numbers
- Leading zeros are prohibited. A decimal point must be followed by at least one
digit.
NaN
andInfinity
are unsupported. - Any JSON text is a valid JavaScript expression...
- ...But only in JavaScript engines that have implemented the proposal to make all JSON text
valid ECMA-262. In engines that haven't implemented the proposal, U+2028 LINE
SEPARATOR and U+2029 PARAGRAPH SEPARATOR are allowed in string literals and property
keys in JSON; but their use in these features in JavaScript string literals is a
SyntaxError
.
Consider this example where JSON.parse()
parses the string as JSON and
Global_Objects/eval
executes the string as JavaScript:
let code = '"\u2028\u2029"'
JSON.parse(code) // evaluates to "\u2028\u2029" in all engines
eval(code) // throws a SyntaxError in old engines
Other differences include allowing only double-quoted strings and having no provisions
for undefined
or comments. For those who wish to use a more human-friendly
configuration format based on JSON, there is JSON5,
used by the Babel compiler, and the more commonly used YAML.
Full JSON syntax
The full JSON syntax is as follows:
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.
Static methods
JSON.parse(text[, reviver])
- Parse the string
text
as JSON, optionally transform the produced value and its properties, and return the value. Any violations of the JSON syntax, including those pertaining to the differences between JavaScript and JSON, cause aSyntaxError
to be thrown. Thereviver
option allows for interpreting what thereplacer
has used to stand in for other datatypes. JSON.stringify(value[, replacer[, space]])
- Return a JSON string corresponding to the specified value, optionally including only
certain properties or replacing property values in a user-defined manner. By default,
all instances of
undefined
are replaced withnull
, and other unsupported native data types are censored. Thereplacer
option allows for specifying other behavior.
Examples
Example JSON
{
"browsers": {
"firefox": {
"name": "Firefox",
"pref_url": "about:config",
"releases": {
"1": {
"release_date": "2004-11-09",
"status": "retired",
"engine": "Gecko",
"engine_version": "1.7"
}
}
}
}
}
Specifications
Browser compatibility
BCD tables only load in the browser