JavaScript Object Notation

JavaScript is a general purpose programming language that was introduced as the page scripting language for Netscape Navigator. It is widely believed to be a subset of Java, but it is not. It is a Scheme-like language with C-like syntax and soft objects. JavaScript was standardized in the ECMAScript Language Specification, Third Edition.

JSON is a subset of the object literal notation of JavaScript. Since JSON is a subset of JavaScript, it can be used in the language with no muss or fuss.

var myJSONObject = {"bindings": [ {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"}, {"ircEvent": "PRIVMSG", "method": "deleteURI", "regex": "^delete.*"}, {"ircEvent": "PRIVMSG", "method": "randomURI", "regex": "^random.*"} ] };

In this example, an object is created containing a single member "bindings", which contains an array containing three objects, each containing "ircEvent", "method", and "regex" members.

Members can be retrieved using dot or subscript operators.

myJSONObject.bindings[0].method // "newURI"

To convert a JSON text into an object, use the eval() function. eval() invokes the JavaScript compiler. Since JSON is a proper subset of JavaScript, the compiler will correctly parse the text and produce an object structure.

var myObject = eval('(' + myJSONtext + ')');

The eval function is very fast. However, it can compile and execute any JavaScript program, so there can be security issues. The use of eval is indicated when the source is trusted and competent. This is commonly the case in web applications when a web server is providing both the base page and the JSON data. There are cases where the source is not trusted. In particular, clients should never be trusted.

When security is a concern it is better to use a JSON parser. A JSON parser will recognize only JSON text and so is much safer:

var myObject = JSON.parse(myJSONtext, filter);

The optional filter parameter is a function that will be called for every key and value at every level of the final result. Each value will be replaced by the result of the filter function. This can be used to reform generic objects into instances of classes, or to transform date strings into Date objects.

myData = JSON.parse(text, function (key, value) {
return key.indexOf('date') >= 0 ? new Date(value) : value;
});

A JSON stringifier goes in the opposite direction, converting JavaScript data structures into JSON text. JSON does not support cyclic data structures, so be careful to not give cyclical structures to the JSON stringifier.

var myJSONText = JSON.stringify(myObject);

If the stringify method sees an object that contains a toJSON method, it calls the method, and stringifies the value returned. This allows an object to determine its own JSON representation.

The stringifier method can take an optional array of strings. These strings are used to select the properties that will be included in the JSON text. Otherwise, all of the properties of the object will be included. In any case, values that do not have a representation in JSON (such as functions and undefined) are excluded.

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JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.

JSON is built on two structures:

• A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
• An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

These are universal data structures. Virtually all modern programming languages support them in one form or another. It makes sense that a data format that is interchangable with programming languages also be based on these structures.

In JSON, they take on these forms:

An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).

An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).

A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.

A string is a collection of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A character is represented as a single character string. A string is very much like a C or Java string.

A number is very much like a C or Java number, except that the octal and hexadecimal formats are not used.

Whitespace can be inserted between any pair of tokens. Excepting a few encoding details, that completely describes the language.

object

{}
{ members }

members

pair
pair , members

pair

string : value

array

[]
[ elements ]

elements

value
value , elements

value

string
number
object
array
true
false
null

---

string

""
" chars "

chars

char
char chars

char

any-Unicode-character-
except-"-or-\-or-
control-character
\"
\\
\/
\b
\f
\n
\r
\t
\u four-hex-digits

number

int
int frac
int exp
int frac exp

int

digit
digit1-9 digits
- digit
- digit1-9 digits

frac

. digits

exp

e digits

digits

digit
digit digits

e

e
e+
e-
E
E+
E-