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:
This credit card has 15 digits. The sequence begins with 34 or 37 and is split among three groups. The first group has four numerals, the second has six and the last g â¦ roup contains five digits. The four digit CVV number is on the front of the card.