What is JSON and why would I use it?

Question

I've looked on wikipedia and Googled it and read the official documentation, but I still haven't got to the point where I really understand what JSON is, and why I'd use it.

I have been building applications using PHP, MySQL and Javascript / HTML for a while, and if JSON can do something to make my life easier or my code better or my user interface better, then I'd like to know about it. Can someone give me a succinct explanation?

Answer 1

the common short answer is: if you are using AJAX to make data requests, you can easily send and return objects as JSON strings. Available extensions for Javascript support toJSON() calls on all javascript types for sending data to the server in an AJAX request. AJAX responses can return objects as JSON strings which can be converted into Javascript objects by a simple eval call, e.g. if the AJAX function someAjaxFunctionCallReturningJson returned

"{ \"FirstName\" : \"Fred\", \"LastName\" : \"Flintstone\" }"

you could write in Javascript

var obj = eval("(" + someAjaxFunctionCallReturningJson().value + ")");
alert(obj.FirstName);
alert(obj.LastName);

JSON can also be used for web service payloads et al, but it is really convenient for AJAX results.

• Update (ten years later): Don't do this, use JSON.parse

Answer 2

JSON is JavaScript Object Notation. It is a much-more compact way of transmitting sets of data across network connections as compared to XML. I suggest JSON be used in any AJAX-like applications where XML would otherwise be the "recommended" option. The verbosity of XML will add to download time and increased bandwidth consumption ($$$). You can accomplish the same effect with JSON and its mark-up is almost exclusively dedicated to the data itself and not the underlying structure.

Answer 3

All of the above answers focus on specifics. So i'll try and explain the concept so you'll be in a position to understand the above.

What is JSON? – How I explained it to my wife^TM

Me: “It’s basically a way of communicating with someone in writing....but with rules.

Wife: yeah....?

ME: Let's take English as an example: we have rules -- full stops, commas, brackets, hyphens, apostrophes etc and they all mean different things. Basically we have all agreed what a full stop means (i.e. we should pause when we read one).

Wife: So are you saying that JSON is a way of writing English to someone, but it has rules which both parties agree upon?

Me: Exactly! Except these rules are very specific. In prosaic English, the rules are pretty loose: just like with cage fighting: you can do whatever you want, except a few basics (e.g. eye gouging). For example, if I wanted to tell the IRS about our family I could do it in a few different using prosaic English. Note the differences in each way:

Me:

• Example 1: Our family has 4 people: You, me and 2 kids.

• Example 2: Our family: you, me, kid1 and kid2.

• Example 3: Family: [ you, me, kid1, kid2]

• Example 4: we got 4 people in our family: mum, dad, kid1 and kid2.

Wife: Ok I get the picture. You can say the same thing many different ways in English. You can add a few words here and there, a few commas here and there and everyone will still understand.

Me: Exactly. Except in JSON, the rules are very restrictive. You can only communicate in a certain way. And you must follow those rules for someone else to understand it: brackets, commas in certain places.

Wife: Why don’t they just use plain English instead?

Me: They would, but remember we’re dealing with computers. A computer is stupid and is not going to be able to understand sentences. So we gotta be really specific when computers are involved otherwise they get confused. Furthermore, JSON is a fairly efficient way of communicating, so most of the irrelevant stuff is cut out, which is pretty hand. If you wanted to communicate our family, to a computer, one way you could do so is like this:

{
                "Family" :  ["Me", "Wife", "Kid1", "Kid2"] 
}

……and that is basically JSON. But remember, you MUST obey the JSON grammar rules. If you break those rules, then a computer simply will not understand (i.e. parse) what you are writing.

Wife: So how do I write in Json?

Me: Read the above answers for specifics. In short, you are forced to communicate things using key-value pairs and arrays.

Summary

JSON is basically a way of communicating data to someone, with very, very specific rules.

Answer 4

In short - JSON is a way of serializing in such a way, that it becomes JavaScript code. When executed (with eval or otherwise), this code creates and returns a JavaScript object which contains the data you serialized. This is available because JavaScript allows the following syntax:

var MyArray = [ 1, 2, 3, 4]; // MyArray is now an array with 4 elements
var MyObject = {
    'StringProperty' : 'Value',
    'IntProperty' : 12,
    'ArrayProperty' : [ 1, 2, 3],
    'ObjectProperty' : { 'SubObjectProperty': 'SomeValue' }
}; // MyObject is now an object with property values set.

You can use this for several purposes. For one, it's a comfortable way to pass data from your server backend to your JavaScript code. Thus, this is often used in AJAX.

You can also use it as a standalone serialization mechanism, which is simpler and takes up less space than XML. Many libraries exists that allow you to serialize and deserialize objects in JSON for various programming languages.

Answer 5

We have to do a project on college and we faced a very big problem, it is called Same Origin Policy. Amog other things, it makes that your XMLHttpRequest method from Javascript can't make requests to domains other than the domain that your site is on.

For example you can't make request to www.otherexample.com if your site is on www.example.com. JSONRequest allows that, but you will get result in JSON format if that site allows that(for example it has a web service that returns messages in JSON). That is one problem where you could use JSON perhaps.

Here is something practical: Yahoo JSON

Answer 6

In short, it is a scripting notation for passing data about. In some ways an alternative to XML, natively supporting basic data types, arrays and associative arrays (name-value pairs, called Objects because that is what they represent).

The syntax is that used in JavaScript and JSON itself stands for "JavaScript Object Notation". However it has become portable and is used in other languages too.

A useful link for detail is here:

http://secretgeek.net/json_3mins.asp