ASP.NET by Example

Client-Side Validation

As mentioned, the validation controls use the WebUIValidation.js file's JScript validation functions to perform validation on browsers that support it. This is referred to as client-side validation and is preferred over server-side validation because it offers the user a better, more responsive experience. It can be very frustrating to have to wait 5 or 10 seconds after each page request, only to find out after each submission that another form element is not valid. By performing all the validation client-side, the user doesn't have the delays that are commonly associated with server-side validation.

However, there are some problems with client-side validation that preclude its use as the sole means of validating user input. ...