What is JSON used for in web applications?

I am relatively new to web development and web applications. I have heard about JSON but am not sure exactly what its uses are.

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JSON is a format for encoding information returned by the server. When you call a script with AJAX/XHR (eg with JavaScript) the returned information can come via XML, JSON, or another format. JSON is simply a way to return that data in an object structure native to JavaScript - in a way that generally doesn't require a lot of parsing, like XML does.

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It is a kind of language for encoding information. For example, if you want to send information about person from one place to another, then it JSON it may look like this:

{
     "firstName": "John",
     "lastName": "Smith",
     "age": 25,
     "address":
     {
         "streetAddress": "21 2nd Street",
         "city": "New York",
         "state": "NY",
         "postalCode": "10021"
     },
     "phoneNumber":
     [
         {
           "type": "home",
           "number": "212 555-1234"
         },
         {
           "type": "fax",
           "number": "646 555-4567"
         }
     ]
 }

Taken from wiki. :) See http://en.wikipedia.org/wiki/JSON for more details.

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First, it's an acronym for JavaScript Object Notation.

It is often used in places where applications deal with object data structures (often seen in languages such as Java, C#, etc.), and associative arrays (key-value pairs seen in many languages such as Python, PHP, etc.)

To answer your question, it's a simple and efficient way to encode objects into strings, transfer them, and recreate the objects on the other end.

JSON on Wikipedia

JSON Homepage

Example of JSON encoding in PHP

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