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
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 grammar
Valid JSON syntax is formally defined by the following grammar, expressed in ABNF, and copied from IETF JSON standard (RFC):
JSON-text = object / array begin-array = ws %x5B ws ; [ left square bracket begin-object = ws %x7B ws ; { left curly bracket end-array = ws %x5D ws ; ] right square bracket end-object = ws %x7D ws ; } right curly bracket name-separator = ws %x3A ws ; : colon value-separator = ws %x2C ws ; , comma ws = *( %x20 / ; Space %x09 / ; Horizontal tab %x0A / ; Line feed or New line %x0D ; Carriage return ) value = false / null / true / object / array / number / string false = %x66.61.6c.73.65 ; false null = %x6e.75.6c.6c ; null true = %x74.72.75.65 ; true object = begin-object [ member *( value-separator member ) ] end-object member = string name-separator value array = begin-array [ value *( value-separator value ) ] end-array number = [ minus ] int [ frac ] [ exp ] decimal-point = %x2E ; . digit1-9 = %x31-39 ; 1-9 e = %x65 / %x45 ; e E exp = e [ minus / plus ] 1*DIGIT frac = decimal-point 1*DIGIT int = zero / ( digit1-9 *DIGIT ) minus = %x2D ; - plus = %x2B ; + zero = %x30 ; 0 string = quotation-mark *char quotation-mark char = unescaped / escape ( %x22 / ; " quotation mark U+0022 %x5C / ; \ reverse solidus U+005C %x2F / ; / solidus U+002F %x62 / ; b backspace U+0008 %x66 / ; f form feed U+000C %x6E / ; n line feed U+000A %x72 / ; r carriage return U+000D %x74 / ; t tab U+0009 %x75 4HEXDIG ) ; uXXXX U+XXXX escape = %x5C ; \ quotation-mark = %x22 ; " unescaped = %x20-21 / %x23-5B / %x5D-10FFFF HEXDIG = DIGIT / %x41-46 / %x61-66 ; 0-9, A-F, or a-f ; HEXDIG equivalent to HEXDIG rule in [RFC5234] DIGIT = %x30-39 ; 0-9 ; DIGIT equivalent to DIGIT rule in [RFC5234]
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
Specification |
---|
ECMAScript Language Specification # sec-json-object |
Browser compatibility
BCD tables only load in the browser