When form input is important, it should always be verified using a secure server-side script.
Otherwise a browser with Java Script disabled, or a hacker trying to compromise your site, can easily submit invalid data. The first test in the example is therefore only necessary in order to provide a different error message when the input is blank.
The purpose of a form validation script is to return a boolean value ('s to reference form fields, but that can lead to namespace conflicts and why make things more complicated than necessary.
When the form is submitted - either by hitting Enter or clicking on the Submit button - the (the 'value' of the field called 'input' belonging to the form). In a real-life situation you will most likely have more fields to check, and more complicated conditions, but the principle remains the same.
It can prevent people from leaving fields blank, from entering too little or too much or from using invalid characters.
For an alternative approach to client-side form validation, without Java Script, check out our new article on HTML5 Form Validation which is available now in most modern browsers.
You can provide custom validation for your forms in two ways: server-side validation and client-side validation.