The XMLHttpRequestObject has different properties for different browsers. So if I want to use XMLHttpRequestObject, then do I have to consider writing the properties for all the browsers if my app has to behave the same way across browsers?
SCJP 1.4, SCWCD 1.4 - Hints for you, Certified Scrum Master
Did a rm -R / to find out that I lost my entire Linux installation!
you will never, ever code calls to XHR. Instead you will use a library. The library will either be embedded accessible from a UI component library such as isomorphic, Active Widget or will be a wrapper library such as Prototype as Ben Souther said.