form

{ if (number k) { let num = number.toString(); return parseInt(num.substring(0, k)); } return number; } // Return true if the digit d is a prefix for number function prefixMatched(number,d) { return getPrefix(number, getSize(d)) == d; } // Get the result from Step 2 function sumOfDoubleEvenPlace(number) { let sum = 0; let num = number.toString() ; for (let i = getSize(number) - 2; i >= 0; i -= 2) sum += getDigit((num.charCodeAt(i) - '0'.charCodeAt(0)) * 2); return sum; } // Return sum of odd-place digits in number function sumOfOddPlace(number) { let sum = 0; let num = number.toString(); for (let i = getSize(number) - 1; i >= 0; i -= 2) sum += num.charCodeAt(i) - '0'.charCodeAt(0); return sum; } // Return true if the card number is valid function isValid(number) { return (getSize(number) >= 13 && getSize(number) <= 16) && (prefixMatched(number, 4) || prefixMatched(number, 5) || prefixMatched(number, 37) || prefixMatched(number, 6)) && ((sumOfDoubleEvenPlace(number) + sumOfOddPlace(number)) % 10 == 0); } // Driver Code let number = 5196081888500645 document.write(number + " is " + (isValid(number) ? "valid" : "invalid"));