14.9 Form Handling^55714.9Form Handling
As you discovered in Chapter 9, the data from a Web form can be submitted to a CGI
or a server-side script. This data can be added to a database or used for some other
purpose; therefore, it is important that the data submitted by a user is as accurate as
possible. When the user enters information in a form, there is always a chance that the
information will be incorrect or inaccurate. This is particularly true when text input
boxes are used, since the user can easily mistype data. Often, the form data is checked
for invalid data before it is submitted. Form data validation can be done by the server-
side script, but it can also be done client-side, using JavaScript. Again, this topic is sim-
plified here, but we can get a sense of how this might be done.
When the user clicks the form’s submit button, the submit event occurs. We can make
use of the onsubmitevent handler to call a function that tests form data for validation.
This technique is referred to as form handling. The Web developer can validate all form
inputs, some inputs, or just one form input. The following list is a selection of some
types of things that might be validated:
●Required fields such as name and e-mail addresses
●A required check box to acknowledge a license agreement
●A radio button indicating method of payment or delivery option
●A quantity entered that is numeric and within a particular rangeWhen the user clicks the submit button, the onsubmitevent handler calls a function
that tests all of the appropriate form elements for valid data. Then the validation func-
tion confirms that the data is valid (true) or not valid (false). The form is submitted
to the URL indicated in the
... XHTML continues
There is a new concept with regard to functions indicated here. A function can encapsu-
late a group of statements, but it can also send a value back to where it was called. This
is referred to as “returning a value” and the JavaScript keyword returnis used in the