JSON

JSON (JavaScript Object Notation) is a format used for transmitting structured data over a network connection in a process called serialization. Its main application is in Ajax web application programming, where it serves as an alternative to the traditional use of XML.


JSON's basic types are

• Number (integer, real, or floating point)
• String (double-quoted Unicode with backslash escapement)
• Boolean (true and false)
• Array (an ordered sequence of values, comma-separated and enclosed in square brackets)
• Object (collection of key/value pairs, comma-separated and enclosed in curly brackets)
• null

The following example shows the JSON representation of an object that describes a person. The object has string fields for first name and last name, contains an object representing the person's address, and contains a list of phone numbers (an array).

{
"firstName": "John",
"lastName": "Smith",
"address": {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": 10021
},
"phoneNumbers": [
"212 732-1234",
"646 123-4567"
]
}

The following Javascript code shows how the client can use an XMLHttpRequest to request an object in JSON format from the server. (The server-side programming is omitted; it has to be set up to respond to requests at url with a JSON-formatted string.)

var the_object;
var http_request = new XMLHttpRequest();
http_request.open( "GET", url, true );
http_request.onreadystatechange = function () {
if ( http_request.readyState == 4 ) {
if ( http_request.status == 200 ) {
the_object = eval( "(" + http_request.responseText + ")" );
} else {
alert( "There was a problem with the URL." );
}
http_request = null;
}
};

More info at http://www.json.org