Form data that typically are checked by a JavaScript could be:
- has the user left required fields empty?
- has the user entered a valid e-mail address?
- has the user entered a valid date?
- has the user entered text in a numeric field?
The idea behind JavaScript form validation is to provide a method to check the user entered information before they can even submit it. JavaScript also lets you display helpful alerts to inform the user what information they have entered incorrectly and how they can fix it. In this lesson we will be reviewing some basic form validation, showing you how to check for the following:
If a text input is empty or not
If a text input is all numbers
If a text input is all letters
If a text input is all alphanumeric characters (numbers & letters)
If a text input has the correct number of characters in it (useful when restricting the length of a username and/or password)
If a selection has been made from an HTML select input (the drop down selector)
If an email address is valid
How to check all above when the user has completed filling out the form
