Javascript - Ajax and Json

What's web service?

A web service is a file or program that can provide data to your web application.

What's Json? 

JSON is short for Javascript Object Notation. It's a data exchange format. Another popular data exchange format is XML. JSON and XML are both capable of representing your application data. Whether to use JSON or XML depends on the type of the data, the web application or the program or web services with which you are exchanging your data with. Typically, JSON is used mostly in web applications. 

Why Json?

• Its format is almost identical to the way you write arrays and objects in javascript, thus more human readable and easier to parse than XML.
• Can be used to convert objects into string, and then store them in a file or send them to web applications/services that are written in different programming languages. 

What's Ajax?

The main goal behind Ajax is to make web pages behaves like a desktop application. Ajax represents a collection of techniques. In a nutshell, it consists of the following steps.

• Requests data from server
• Stays on the current page and waits for the response while still be able to interact with user
• Receives data from the server and updates only parts of the page.

The most important feature of Ajax is it enables the page to send and receive data from the server without causing the page to hang or reload. As mentioned before, the goal of Ajax is to make web pages behave like a desktop application. The flow of user interaction is the most important and should not be interrupted by page hanging or reloading. Ajax solves this problem. 

What's Cross-Domain Security Restriction?

For example, if you are running a web application at the URL http://example.com/my_app.html, you can only request data that is being served from the domain example.com. This restriction is supposed to keep malicious data out of your application.