People entering the numbers may have different ideas yet. Visa and MasterCard put digits in sets of 4, while Amex and Discover use groups of 4, 5 and 6 digits. This regex allows any amount of spaces and dashes anywhere in the number. All these regexes were taken from RegexBuddy’s library. It is most notably used to validate credit card numbers and IMEI phone identification numbers. The Luhn algorithm, a simple checksum verification algorithm, is also known as Luhn formula, modulus 10 algorithm, or mod 10 algorithm. Fill in the box below to have it instantly computed. You can use the specific regular expressions below to alert customers when they try to use a kind of card you don’t accept, or to route orders using different cards to different processors. Calculate check digit using the Luhn algorithm. They’re just a sequence of 13 to 16 digits, with a few specific digits at the start that identify the card issuer. Validating credit card numbers is the ideal job for regular expressions. Validating Credit Card Numbers on Your Order Form Though the savings are minimal here, so is the effort of typing the extra plus. But it’s a good habit to keep regex efficiency in the back of your mind. In this case, the savings are only a few microseconds. Without the plus, three replacements would be required. You can download the library at You can see this library in action on our credit card validator tool. If the input has consecutive non-digits, such as 1=2, then + matches the three equals signs at once and deletes them in one replacement. Our recommended JavaScript credit card validation library is the JQuery Credit Card Validator, open source software which implements both Luhn verification and limited IIN lookups. If you’re wondering what the plus is for: that’s for performance. If this regex looks odd, remember that in a character class, the hyphen is a literal when it occurs right before the closing bracket (or right after the opening bracket or negating caret). If you only want to replace spaces and dashes, you could use +. To remove all non-digits from the card number, simply use the “replace all” function in your scripting language to search for the regex + and replace it with nothing. So your order form should accept card numbers with spaces or dashes in them. Physical credit cards have spaces within the card number to group the digits, making it easier for humans to read or type in. The first step is to remove all non-digits from the card number entered by the customer. This can be very useful to prove in a security audit that you’re not improperly exposing your clients’ financial details. You can use a slightly different regular expression to find credit card numbers, or number sequences that might be credit card numbers, within larger documents. Each card issuer has its own range of card numbers, identified by the first 4 digits. You can even determine the type of credit card being used. This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development.With a few simple regular expressions, you can easily verify whether your customer entered a valid credit card number on your order form. Hopefully, that should help you locate which part of that code has a problem, and what the problem is. Did it do what you expect? If so, move on to the next line. Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to). When it reaches the breakpoint, the debugger will stop, and hand control over to you. Put a breakpoint on the first line of the method, and run your app. Once you have an idea what might be going wrong, start using the debugger to find out why.
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