There are two factors to consider when deciding how to handle the problem of a work sample: sample size and population characteristics. Sample size is determined by a formula based on the power of the sample or its ability to represent the population with a predictable margin of error.
The resulting complexity makes card type detection code difficult to write, read, and maintain. As an example of this complexity, consider this JavaScript regular expression used to detect Discover card numbers starting with 6011, 622126-622925, 644-649, and 65:
Here are what some of the numbers stand for: The first digit in your credit-card number signifies the system 1  : 3 - travel/entertainment cards (such as American Express and Diners Club).2  4 - Visa. 3  5 - MasterCard.4  6 - Discover Card.he first digit in your credit-card number signifies the system 1  : 3 - travel/entertainment cards (such as American Express and Diners Club). 2  4 - Visa. 3  5 - MasterCard. 4  6 - Discover Card.