# JavaScript: Implement the Luhn Algorithm used to validate a variety of identification numbers

## JavaScript fundamental (ES6 Syntax): Exercise-80 with Solution

Write a JavaScript program to implement the Luhn Algorithm used to validate identification numbers. For example, 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.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
// Define the function 'luhnCheck' to perform the Luhn algorithm check on a given number.
const luhnCheck = num => {
// Convert the number to a string, split it into an array of digits, reverse the array, and convert each digit to an integer.
let arr = (num + '').split('').reverse().map(x => parseInt(x));
// Extract the last digit from the array.
let lastDigit = arr.splice(0, 1)[0];
// Calculate the Luhn sum using the Luhn algorithm.
let sum = arr.reduce((acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val * 2) % 9) || 9), 0);
// Add the last digit to the sum.
sum += lastDigit;
// Check if the sum is divisible by 10.
return sum % 10 === 0;
};

// Example usages:
console.log(luhnCheck('4485275742308327'));
console.log(luhnCheck(6011329933655299));
console.log(luhnCheck(123456789));
```
```

Output:

```true
false
false
```

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-80-1 by w3resource (@w3resource) on CodePen.

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