1. What is the alternatives of JSONP?
The easiest alternative is setting up a proxy to an external API through the same origin as the web application. This can be done pretty easily using tooling built into web servers like Apache and Nginx.
2. Suppose some one says that we do not need to use JSONP then?
Deciding against using JSONP is directly related to how it works. First of all, the only HTTP method you can use is GET since that is the only method script tags support. This immediately eliminates the use of JSONP as an option to interact with nice RESTful APIs that use other HTTP verbs to do fun stuff like CRUD.
3. Why we need to use the JSONP?
JSONP is universally supported on just about every browser and a lot of useful APIs have support for it already in place (Yahoo, Twitter, Google, etc.) Aside from the regular XMLHttpRequest and DOM differences, nothing really special needs to be done to make it work across different browsers. Finally, since it has been around for a bit, there are pretty mature JSONP plugins for just about every major library and framework around (JQuery, YUI, Prototype, etc.)
JSONP is a communication technique used in JavaScript programs which run in Web browsers. It provides a method to request data from a server in a different domain, something prohibited by typical web browsers because of the same origin policy.
