31 lines
1.0 KiB
Markdown
31 lines
1.0 KiB
Markdown
---
|
|
title: luhnCheck
|
|
tags: math,advanced
|
|
---
|
|
|
|
Implementation of the [Luhn Algorithm](https://en.wikipedia.org/wiki/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()` and `Array.prototype.map()` in combination with `parseInt()` to obtain an array of digits.
|
|
Use `Array.prototype.splice(0,1)` to obtain the last digit.
|
|
Use `Array.prototype.reduce()` to implement the Luhn Algorithm.
|
|
Return `true` if `sum` is divisible by `10`, `false` otherwise.
|
|
|
|
```js
|
|
const luhnCheck = num => {
|
|
let arr = (num + '')
|
|
.split('')
|
|
.reverse()
|
|
.map(x => parseInt(x));
|
|
let lastDigit = arr.splice(0, 1)[0];
|
|
let sum = arr.reduce((acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val * 2) % 9) || 9), 0);
|
|
sum += lastDigit;
|
|
return sum % 10 === 0;
|
|
};
|
|
```
|
|
|
|
```js
|
|
luhnCheck('4485275742308327'); // true
|
|
luhnCheck(6011329933655299); // false
|
|
luhnCheck(123456789); // false
|
|
```
|