Luhn check
JavaScript, Math, Algorithm · Jan 30, 2022
Implements the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.
- Use
String.prototype.split(),Array.prototype.reverse()andArray.prototype.map()in combination withparseInt()to obtain an array of digits. - Use
Array.prototype.shift()to obtain the last digit. - Use
Array.prototype.reduce()to implement the Luhn Algorithm. - Return
trueifsumis divisible by10,falseotherwise.
const luhnCheck = num => {
const arr = (num + '')
.split('')
.reverse()
.map(x => parseInt(x));
const lastDigit = arr.shift();
let sum = arr.reduce(
(acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val *= 2) > 9 ? val - 9 : val)),
0
);
sum += lastDigit;
return sum % 10 === 0;
};luhnCheck('4485275742308327'); // true
luhnCheck(6011329933655299); // true
luhnCheck(123456789); // false
