Why need to use JSON in php and AJAX - php

Question

I just started doing jQuery last week, and so far I already made some basic systems with ajax, like basic jQuery CRUD and simple chat system without referencing on other's work for I decided to test myself on how far I can do systems alone in jQuery(without JSON and XML yet).
But when I decided to look at other's work (hoping to get/learn good practices and codes out there) many or almost every program that deals with ajax have some JSON in it. So I decided to study and read JSON specially this one, but I guess because it's my first time dealing with it, I'm having a problem sinking it into my brain. Yeah I know it is a "lightweight way of describing hierarchical data", I also know how to make JSON like mixing a literal array and object in JS, and how to dsplay it in js.
But my question is, what's the difference and what's the advantage than not using it?
When I can still get and store data on the server using ajax and database without JSON.
By the way I haven't focus on XML yet because based from my research it's better to use JSON in AJAX.
Can you give me some actual scenario dealing with
s1. ajax php mysql (this with what disadvantages?)
and
s2. ajax php mysql json (this with what advantages?)
I mean, my focus is to send and get data, and I already can do it with s1.
Sorry if you find my question stupid. Tia. :)

Answer 1

Why use JSON? The answer is portability and structure.
JSON is portable because parsers and writers are available for many, many languages. This means that JSON that a PHP script generates can be very easily understood by a JavaScript script. It is the best way to transmit complex structures like arrays and objects, and have it still be compatible with multiple languages.
JSON provides structure because the data you transmit with it can have consistent formatting. This is instead of transmitting back plain-text (i.e. unformatted) data, like comma-separated or delimited data.
Data that is merely delimited (for example, "BookName1,BookName2,BookName3") is more difficult for humans to understand, debug, and work with. If you wanted to debug a response between your server and your browser and the data was delimited (like my example above), you might have a hard time understanding it. Also, if you want to add different data types, provide separate records, etc., then your custom data format becomes more complicated. Eventually, you might end up reinventing JSON.
As a side note, JSON is indeed better than XML. It is much more efficient space-wise. There are no tag names to take up space. Structure is created via nested braces, instead of verbose tags.
Resources
Here is an interesting article on the differences and pros/cons of XML and JSON: http://www.json.org/xml.html
Examples
Per your request, here is an example of encoding JSON with PHP. This is ripped from the docs:
$arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);
echo json_encode($arr);
Output:
{"a":1,"b":2,"c":3,"d":4,"e":5}
Contrast this to something like this, without JSON:
a,1
b,2
c,3
d,4
e,5
To parse that, you'd have to iterate through each line, split the values yourself, and then create the array. This isn't that difficult, but imagine you have a nested object:
$arr = array ('a'=> array(1,2,3),'b'=> array('a' => 1, 'b' => 2),'c'=>3,'d'=> array(1,2,3,4,5) ,'e'=>5); // etc.
With JSON, it's no different to encode it. Just use json_encode. But, encoding this manually, and then decoding it manually would be significantly more work.

Answer 2

Programming in any sort of programming language, you have several different types of data at your disposal, including the very useful array type.
Interchanging data between Javascript and any server side language can only happen through strings. I.e. you can send and return any text, but there's no way to send a native array or number type.
JSON is an elegant way to express array and other types using only a string. This way you can pass arbitrary data back and forth between different environments and are not limited to pure text. XML solves the same kind of problem, but is often overkill for simple AJAX requests.