Luhn’s Algorithm - Credit Card # Check.

check.js

// test cards 
// https://developer.paypal.com/docs/classic/payflow/payflow-pro/payflow-pro-testing/#credit-card-numbers-for-testing

const card = 378282246310005;
let mod = 1;
let flag = true;
let sum = 0;
const digits = 16;


for (let i = 1; i <= digits; i++ ) {
  let num = Math.floor((card / mod) % 10);
  if ((flag = !flag)) {
    num *= 2;
  }
  if ( num > 9) {
    num -= 9;
  }
 
  mod *= 10;
  sum += num;
}

if (sum % 10 === 0)
    {
       console.log("VALID CARD");
      // here do another check for issuer;
    } 
else 
    {
        console.log("INVALID CARD");
    }