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.For these examples we have created our own valid/invalid CSS formatting to override the browser default. That's why you may see something like the following: Before you type anything into the box a red marker is shown.As soon as a single character has been entered this changes to a green marker to indicate that the input is 'valid'.Different browsers may mark the input box in some way (Firefox 4 Beta adds a red box-shadow by default), display a warning (Opera) or even prevent the form from being submitted if this field has no value.Hopefully these behaviours will converge in future releases.
We use Java Script for Client-Side Validation and PHP for Server-Side Validation. You can do more validation on Client-Side as per your need to make your code more secure.
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 .
Again, not very helpful, but it will stop people trying to input their email address or other such nonsense. Careful examination of the RFCs associated with email addresses has been conducted repeatedly and has been proven to require the use of recursion in order properly determine the validity of an email address using the full set of RFC specifications.
As mentioned above, we can improve on this by making use of the are already implicit so the input has to match the entire expression. If anyone wants to contribute a more thorough expression to test for valid email or url format, feel free to post it using the Feedback option above.. Since it is not possible to recurse when using a regular expression it is also not possible to create a truly accurate regex for doing email address validation.