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:
One can tell that a credit card is a VISA card if the first digit of the card number begins with a 4.There are, however, a few exceptions including the following: 4903 4905 â¦ 4911 4936. 10 people found this useful.James Yee.here are several ways to tell if a credit card number is a Visa card number or not. First, Visa numbers always start with the number 4. They are also usually 13 or 16 digits â¦ in length.. 5 people found this useful.