Regular expression or RegEx may look like a simple function in an Ajax or JavaScript based application but it’s presence in these forms of applications is very importance since they help in screening the forms of data coming into the application. The common forms of Regular Expression will screen if the data is created according to the specifications of the developers. But there are other additional functions in RegEx that proactively work with the data provided by users or actively change the data found in the application. Through these functions, developers would be able to build or customize regular expressions according to the specifications of developers. The fo