Designing Active Server Pages

Form Validation

With ASP, information collected through a form interface is often used to modify a database in some way. Databases are only as good as the data within them. A database saturated with meaningless or improperly formatted data is worthless. Therefore, when creating ASP pages that will directly modify databases based upon input gathered through a form, it is vital that the user entering the form information enters valid data.

The process of ensuring that form fields contain valid input is referred as form validation. Form validation can occur on both the client side and server side. In the next two sections, Section 5.3.1 and Section 5.3.2, we’ll discuss the advantages and disadvantages of each method.

Client-Side Form Validation

Client-side form validation, as the name implies, is form validation that happens on the client. A web page containing a form can optionally contain client-side JavaScript code that will execute when the user attempts to submit the form. This JavaScript code can then scan the user’s form entries, making sure they have a particular format.

The main advantage of client-side form validation is the fact that the validation occurs completely on the client’s computer. Therefore, if the user has entered invalid form data, they don’t have to wait for a round trip to the web server before they know whether or not they’ve entered invalid data. Many sites employ this type of form validation. For example, an e-commerce site might provide form validation for ...