In all cases, the form is called That's checking the value's equality with a null String (two single quotes with nothing between them).When you are asking a reader for their email address, you can use a simple » address validation function to make sure the address has a valid structure. Each option in a drop-down box is indexed in the array Annoyingly, there is no simple way to check which radio button out of a group is selected — you have to check through each element, linked with Boolean AND operators .
When you submit a form to a CGI program that resides on the server, it is usually programmed to do its own check for errors.
If it finds any it sends the page back to the reader who then has to re-enter some data, before submitting again.
This tutorial will show you how to create a Java Script-enabled form that checks whether a user has filled in the form correctly before it's sent to the server. First we'll explain why form validation is a useful thing, and then build up a simple example form, explaining things as we go along.
At the end, there's a little exercise to keep you busy too!
When the user does so, they may proceed and can supply value to the next available field.
The later Java Script function created is called on the onsubmit event of the form. If Male or Female is selected, it generates an alert saying that the form is successfully submitted and it reloads the form.
We're going to be checking the form using a function, which will be activated by the form's Validating this form would be considerably simpler than one containing radio buttons or select boxes, but any form element can be accessed.
Below are the ways to get the value from all types of form elements.
Form validation is the process of checking that a form has been filled in correctly before it is processed.