http://www.w3schools.com/json/json_files.asp

Much Like XML Because

    Both JSON and XML are "self describing" (human readable)
    Both JSON and XML are hierarchical (values within values)
    Both JSON and XML can be parsed and used by lots of programming languages
    Both JSON and XML can be fetched with an XMLHttpRequest

Much Unlike XML Because

    JSON doesn't use end tag
    JSON is shorter
    JSON is quicker to read and write
    JSON can use arrays

The biggest difference is:

 XML has to be parsed with an XML parser. JSON can be parsed by a standard JavaScript function.
Why JSON?

For AJAX applications, JSON is faster and easier than XML:

Using XML

    Fetch an XML document
    Use the XML DOM to loop through the document
    Extract values and store in variables

Using JSON

    Fetch a JSON string
    JSON.Parse the JSON string

JSON Syntax Rules

JSON syntax is derived from JavaScript object notation syntax:

    Data is in name/value pairs
    Data is separated by commas
    Curly braces hold objects
    Square brackets hold arrays

JSON Data - A Name and a Value

JSON data is written as name/value pairs.

A name/value pair consists of a field name (in double quotes), followed by a colon, followed by a value:
Example

    "firstName":"John"

JSON names require double quotes. JavaScript names don't.
JSON Values

JSON values can be:

    A number (integer or floating point)
    A string (in double quotes)
    A Boolean (true or false)
    An array (in square brackets)
    An object (in curly braces)
    null

JSON Objects

JSON objects are written inside curly braces.

Just like JavaScript, JSON objects can contain multiple name/values pairs:

Example
    {"firstName":"John", "lastName":"Doe"}

JSON Arrays

JSON arrays are written inside square brackets.

Just like JavaScript, a JSON array can contain multiple objects:
Example
    "employees":[
        {"firstName":"John", "lastName":"Doe"},
        {"firstName":"Anna", "lastName":"Smith"},
        {"firstName":"Peter","lastName":"Jones"}
    ]

In the example above, the object "employees" is an array containing three objects. Each object is a record of a person (with a first name and a last name).
JSON Uses JavaScript Syntax

Because JSON syntax is derived from JavaScript object notation, very little extra software is needed to work with JSON within JavaScript.

With JavaScript you can create an array of objects and assign data to it, like this:
Example
    var employees = [
        {"firstName":"John", "lastName":"Doe"},
        {"firstName":"Anna", "lastName":"Smith"},
        {"firstName":"Peter","lastName": "Jones"}
    ];

The first entry in the JavaScript object array can be accessed like this:
Example
    // returns John Doe
    employees[0].firstName + " " + employees[0].lastName;

It can also be accessed like this:
Example
    // returns John Doe
    employees[0]["firstName"] + " " + employees[0]["lastName"];

Data can be modified like this:
Example
    employees[0].firstName = "Gilbert";

It can also be modified like this:
Example
    employees[0]["firstName"] = "Gilbert";

In the next chapter you will learn how to convert a JSON text to a JavaScript object.
JSON Files

    The file type for JSON files is ".json"
    The MIME type for JSON text is "application/json"

JSON Example - Object From String

Create a JavaScript string containing JSON syntax:

    var text = '{ "employees" : [' +
    '{ "firstName":"John" , "lastName":"Doe" },' +
    '{ "firstName":"Anna" , "lastName":"Smith" },' +
    '{ "firstName":"Peter" , "lastName":"Jones" } ]}';

JSON syntax is a subset of JavaScript syntax.

The JavaScript function JSON.parse(text) can be used to convert a JSON text into a JavaScript object:

    var obj = JSON.parse(text);

Use the new JavaScript object in your page:
Example
    <p id="demo"></p>

    <script>
    document.getElementById("demo").innerHTML =
    obj.employees[1].firstName + " " + obj.employees[1].lastName;
    </scipt>