30-seconds-of-code/snippets/luhnCheck.md

luhnCheck

Implementation of the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc. Works with numbers and strings alike

const luhnCheck = num => { 
    let arr = (num+'').split('').reverse()
    let lastDigit = arr.splice(0,1)
    let sum = arr.reduce((acc,val,i) => {
	    val = parseInt(val)
    	if(i%2!==0) return acc + val
    	else{
		    val = (val * 2)%9 || 9
		    return acc+ val }
        },0)
     sum += parseInt(lastDigit)
     return sum%10 === 0
 }

 luhnCheck("4485275742308327"); //true
 luhnCheck(4485275742308327); //true
 luhnCheck(6011329933655299); // true
 luhnCheck(123456789); //false