Luhn's Algorithm

index.js

// https://x.com/cneuralnetwork/status/1831989042826629546

const digits = "4137894711755904";

let sum = [];
digits.split("").map((digit, index) => {
  if (index % 2 === 0) {
    const double = +digit * 2;
    if (double > 9) {
      let pushItem = String(double)
        .split("")
        .reduce((a, b) => +a + +b);
      sum.push(pushItem);
    } else {
      sum.push(double);
    }
  } else {
    sum.push(+digit);
  }
});
console.log(
  String(sum.reduce((a, b) => a + b, 0)).endsWith("0") ? "Valid" : "Invalid"
);