JSON
The JSON namespace object contains static methods for parsing values from and converting values to JavaScript Object Notation (JSON).
Description
Unlike most global objects, JSON is not a constructor. You cannot use it with the new operator or invoke the JSON object as a function. All properties and methods of JSON are static (just like the Math object).
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 JavaScript: most of JavaScript is not JSON. For example:
Property names must be double-quoted strings; trailing commas are forbidden.
Leading zeros are prohibited. A decimal point must be followed by at least one digit. NaN and Infinity are unsupported.
Any JSON text is a valid JavaScript expression, but only after the JSON superset revision. Before the revision, U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR are allowed in string literals and property keys in JSON; but the same use in JavaScript string literals is a SyntaxError .
Other differences include allowing only double-quoted strings and no support 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.
The same text may represent different values in JavaScript object literals vs. JSON as well. For more information, see Object literal syntax vs. JSON.
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 properties
The initial value of the @@toStringTag property is the string «JSON» . This property is used in Object.prototype.toString() .
Static methods
Parse a piece of string text as JSON, optionally transforming the produced value and its properties, and return the value.
Return a JSON string corresponding to the specified value, optionally including only certain properties or replacing property values in a user-defined manner.
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" > > > > >
You can use the JSON.parse() method to convert the above JSON string into a JavaScript object:
const jsonText = ` < "browsers": < "firefox": < "name": "Firefox", "pref_url": "about:config", "releases": < "1": < "release_date": "2004-11-09", "status": "retired", "engine": "Gecko", "engine_version": "1.7" >> > > >`; console.log(JSON.parse(jsonText));
Specifications
Browser compatibility
BCD tables only load in the browser
See also
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This page was last modified on Jul 24, 2023 by MDN contributors.
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