South African ID validation

validateId.js

function validateZARID(id) {

  if (!id || typeof id !== 'string') {
    return;
  }

  id = id.split('');

  const validationCheck = [];
  let sum = 0;

  for (let i = 0; i < id.length; i++) {
  
    // double every second digit.
    if (i % 2 === 1) {
    
      const multiplyNumber = Number(id[i]) * 2;

      // check for double numbers
      if (multiplyNumber && multiplyNumber.toString().length > 1) {
        
        const [n1, n2] = multiplyNumber.toString().split('');
        const singleDigit = Number(n1) + Number(n2);

        validationCheck.push(singleDigit);

        continue;
      }

      validationCheck.push(multiplyNumber);

      continue;
    }

    validationCheck.push(Number(id[i]));
  }

  for (let i = 0; i < validationCheck.length; i++) {
    sum += validationCheck[i];
  }

  return sum === 0 ? false : !(sum % 10);
}