Using the onkeypress event, we could create on-the-fly form validation. The idea is to use the onkeypress event handler inside the form field to check, so as the user types, it is being validated concurrently.Here's an example that limits a form field to contain only numeric input (on the fly, of course! Try typing in stuff other than numbers into the above box- you can't. By checking to see whether the keycode of the key pressed as the user types falls within the range of the number keys (48~57), and if not, returns false, which disables the keypress action.How did I know 48 to 57 represents the keycode of the numeric keys?Client side validations become very important when submitting data on a web page. We have an input box and it must accept only numbers, and it should not allow other characters as input.
This is why it's important to do both server side and client side validation.ASP can perform numeric validation, but only once all the data has been submitted to the server, then the user must correct any invalid fields and resubmit the page.A better solution is to use Java Script to validate each field on the client browser as the user enters data and if necessary carry out any mathematical calculation, without the need to submit the page, thereby speeding up the data entry process.DTHML and scripting languages improve things somewhat.
It is possible to provide the user with immediate feedback on bad input and to prevent them from posting a page until it has been corrected.