The idea behind Java Script form validation is to provide a method to check the user entered information before they can even submit it.
Java Script also lets you display helpful alerts to inform the user what information they have entered incorrectly and how they can fix it.
If someone is entering a credit card, phone number, zip code, similar information you want to be able to ensure that the input is all numbers.
The quickest way to check if an input's string value is all numbers is to use a regular expression /^[0-9] $/ that will only match if the string is all numbers and is at least one character long.
As a PRO member, you can drag-and-drop upload files here to use as resources.