Check Username availability using AJAX and JavaScript

Here Mudassar Ahmed Khan has explained with an example, how to check Username availability i.e. check whether Username exists in database or not using JavaScript XML HTTP function and AJAX and in ASP.Net with C# and VB.Net. This article will illustrate how to check Username availability in database on Registration Form by making AJAX call to database using JavaScript XML HTTP function and WebMethod in ASP.Net with C# and VB.Net.