One of the more important uses of JavaScript is to validate user input prior to sending the data to a receiving program at the server end. This is significant for several reasons:

• It reduces load on the server. Invalid data are already filtered out when input is passed to the program.
• The user gets quicker responses, as the validation is performed on the client-side. The data does not have to be sent back for correction.
• It simplifies the server-based program.

Basically, an author can choose to validate input in two levels:

1. at the field-level, as the user inputs the data, by assigning a handler to either:
   • the onchange event attribute of each form element that you want validated;
   • any of the keyboard events attribute possible for the given field.
2. at the form-level, when the user submits the form, by assigning a handler to either:
   • the onclick event attribute of the button that submits the form;
   • the onsubmit event attribute of the form itself.

This section lists the basic set of form validation routines that are covered in this workshop:

• Check if all form fields are filled out
• Check for letters ( alphabet entries only )
• Check for numbers ( numeric entries only )
• Check for a valid range of values
• Force a number input to n decimal places
• Check for a valid date input
• Check for valid email addresses

Web Forms Validation