SUMMARY
Ajax is a method for retrieving data from the server without refreshing the current page. Ajax has the following characteristics:
- The central object responsible for the growth of Ajax is the
XMLHttpRequest(XHR) object. - This object was created by Microsoft and first introduced in Internet Explorer 5 as a way to retrieve XML data from the server in JavaScript.
- Since that time, Firefox, Safari, Chrome, and Opera have all duplicated the implementation, and the W3C has written a specification defining the XHR behavior, making XHR a Web standard.
- Though there are some differences in implementations, the basic usage of the XHR object is relatively normalized across all browsers and can therefore safely be used in web applications.
One of the major constraints on XHR is the same-origin policy that limits communication to the same domain, using the same port, and with the same protocol. Any attempts to access resources outside of these restrictions cause a security error, unless an approved...
