Verifying Well-Formed Credit Card Numbers
The only way to completely verify the validity of a credit card number is through a Web server specifically set up to handle credit card transactions. However, you can use JavaScript to apply some checks at the client-side that enable you to determine whether the number is well formed. A well-formed number is one that could be a valid number for that type of credit card. Passing the test for being well formed does not mean that the number is from a good credit card; failing the test, however, does mean that the number can't be from a good card.
You can apply two easy tests using JavaScript at the client-side. These tests enable you to determine whether a credit card number for a given card type is well ...
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