This post will walk through JSON basic concepts.

What is JSON?

JSON (JavaScript Object Notation) is a lightweight data-interchange format, widely hailed as the successor to XML in the browser.

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.

It is lighter than XML.

JSON versus XML

Ps.: This is only from the javascript eval() point of view.

JSON	XML
JSON object are type	XML data is typeless
JSON types: string, number, array, boolean	XML data are all string
Data is readily accessible as JSON objects	XML data needs to be parsed
Retrieving value is easy	Retrieving value is difficult
JSON is supported by all browsers	Cross browser XML parsing can be tricky
Simple API	Complex API
Supported by many Ajax toolkit	Not fully supported by Ajax toolkit
Fast object de-serialization in JavaScript	Slower de-serialization in Javascript
Fully automated way of de-serializing/serializing JavaScript objects	Developers have to write javascript code to serialize/se-serialize to/from XML

JSON Values

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.

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.

JSON Syntax

• For objects start the object with “{“ and end it with “}”
• For members (properties), use pairs of string : value and separate them by commas
• For arrays put the arrays between []
• For elements put the values directly separated by commas

Example:

<script type="text/javascript">
var myFirstJSON = { "firstName" : "Loiane",
                    "lastName"  : "Groner",
                    "age"       : 23 };

document.writeln(myFirstJSON.firstName);  // Outputs Loiane
document.writeln(myFirstJSON.lastName);   // Outputs Groner
document.writeln(myFirstJSON.age);        // Outputs 23
</script>

This object has 3 properties or name/value pairs. The firstName and lastName are strings and age is a number.

The value can be any Javascript object (and remember everything in Javascript is an object so the value can be a string, number, array, function, even other Objects).

<script type="text/javascript">
var hobbies = { "tvseries" :
			[ //array
				{"name": "Lost", "seasons":5 },
				{"name": "Heroes", "seasons":4 },
				{"name": "Fringe", "seasons":2 },
				{"name": "The Office", "seasons":5 },
				{"name": "The Big Bang Theory", "seasons":3 },
				{"name": "True Blood", "seasons":2 },
				{"name": "Battlestar Galactica", "seasons":4 },
				{"name": "Sex and the City", "seasons":6 },
				{"name": "Friends", "seasons":10 }
			]
			"games" :
				[
				"Counter Strike" ,"Sacred 2","The Sims 3","Guitar Hero"
				]

      		};

document.writeln(hobbies.tvseries[0].name); // Outputs Lost
document.writeln(hobbies.games[3]); 	   // Outputs Guitar Hero
</script>

hobbies is an object. That object has two properties or name/value pair (tvseries and games).

tvseries is an array which holds two JSON objects showing the names and seasons of 9 TV Series. Likewise games is also an array which holds four JSON objects showing the names of games I like.

Well, this is just a start. You can study JSON functions and how to convert JSON objects now. You can also study Ajax toolkits taht support JSON.

Happy coding!