What is json,can you explain it to a newbie?

Question

Can you explain it in most simple words?

Best with a demo script.

Answer 1

JSON is a way of sharing data (usually between the browser and a server).

JavaScript allows for two way to store collections of values:

//arrays:
[value, value, value]
//objects:
{key:value, key:value, key:value}

At some point, a guru known as Doug realized that it is usually most efficient to send data to JavaScript already setup like an object. [Rather than PHP sending a comma-delimited strings, post-data, XML, or even HTML, all of which have to be painstakingly parsed by the JavaScript].

So he called that idea JSON, wrote up a spec for it, and the standard was born.

For example, let's say your login.php script should return the users name, total posts, and days since registered:

//XML
"<xml..><details>\
    <user>Jim</user><posts>239</posts><since>Jan09</since>\
</details>"
//POSTData
"user=Jim&posts=239&since=Jan09"
//JSON
"{user:'Jim', posts:239, since:'Jan09'}"

The last one can be easily parsed by JS (using eval), and the details can be used intuitively:

var user = details.user;

EDIT:

It was correctly noted that to be valid JSON, all strings must be double quoted. This was done to prevent JS from croaking on reserved keywords (in JS one may not use certain words, such as class, unless they are quoted. So {class:'mike'} cannot be used).

It should also be pointed out that PHP 5.2+ has functions which can be used to create or parse JSON:

<?php
    $arr = array ('a'=>'ay','b'=>'bee','c'=>'cee');
    echo json_encode($arr); //outputs {"a":"ay","b":"bee","c":"cee"}
?>

The json_decode function will ONLY work if the JSON is valid, so it is sometimes important to get those double-quotes right.

Answer 2

It's basically a way of describing objects in text - a text-based serialization format. However, the beauty of it is that it's also just normal JavaScript. The syntax of JavaScript allows objects to be initialized in a pretty concise format, and that format is fairly easy to generate/parse in other languages too.

So, you get "built-in" deserialization in JavaScript (i.e. you can just interpret the text as code¹) with no extra libraries, and other platforms can create it, usually with a library. (Typically a web server will generate JSON for a browser to interpret.)

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¹ This assumes you trust your data source completely, of course - executing arbitrary text as code is pretty dangerous from a security standpoint.