Form Validation

Every interactive site or blog has at least one form, a place where users are required to enter various data: name, email, address, comments, suggestions etc. The data that is entered in the form is passed to a script (usually ASP script, PHP script or Perl script) which stores the data in a database, or sends the form submission to a certain email address. If the form is used to create a connection between the user and the site owners, it is very important that the filled data is accurate. For example, if a form requires the user's telephone number, and an Italian visitors enters 003i771456201 instead of 0039771456201, the form submission becomes useless. This is why HTML form validation appeared: to make sure the data submitted using the forms is accurate, and does not contain typos that could make the submissions unusable.

Form Validation Scripts

There are two categories of form validation scripts: client-side scripts (usually JavaScript) and server-side scripts. JavaScript form validation is instantaneous, but it becomes useless if the visitor' browser has JavaScript disabled. It is also quite difficult to implement and debug, which makes it not a good option for the beginner site owner. Server-side scripts do not have compatibily issues. They validate the fields using clear rules, and, if the data is not valid it displays an error message, asking the user to make the necesary corrections.

123ContactForm solution

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Below you can see a sample newsletter subscription form that uses form validation. Please enter some values to those fields, and click the button, to see how the form validation works.