Validate a Canadian Social Insurance Number (SIN)

validateSIN.js

/**
 * Validate a Canadian Social Insurance Number (SIN)
 * @param  {num || str} sin   A 9-digit Canadian SIN
 * @return {bool}             Validity of the input SIN
 */
function validateSIN (sin) {
  var check, even, tot;

  if (typeof sin === 'number') {
    sin = sin.toString();
  }

  if (sin.length === 9) {
    // convert to an array & pop off the check digit
    sin = sin.split('');
    check = +sin.pop();

    even = sin
      // take the digits at the even indices
      .filter(function (_, i) { return i % 2; })
      // multiply them by two
      .map(function (n) { return n * 2; })
      // and split them into individual digits
      .join('').split('');

    tot = sin
      // take the digits at the odd indices
      .filter(function (_, i) { return !(i % 2); })
      // concatenate them with the transformed numbers above
      .concat(even)
      // it's currently an array of strings; we want numbers
      .map(function (n) { return +n; })
      // and take the sum
      .reduce(function (acc, cur) { return acc + cur; });

    // compare the result against the check digit
    return check === (10 - (tot % 10)) % 10;
  } else throw sin + ' is not a valid sin number.';
}

thank you!

Thank you very much, this is helpful

Apparently this is known as the Luhn algorithm

Another implementation of the check

/**
 * Validate a Canadian Social Insurance Number (SIN)
 * @param  {num || str} sin   A 9-digit Canadian SIN
 * @return {bool}             Validity of the input SIN
 */
function validateSIN (sin) {
  let multiplyEveryOtherBy2 = (val, index) => val *((index%2)+1) ;
  let sumValues = (acc,val)=>acc+parseInt(val);

  if (typeof sin === 'number') {
    sin = sin.toString();
  }

  if (sin.length !== 9) {
   console.log("Wrong length");
    return false;
  }

  // convert to an array & pop off the check digit
  sin = sin.split('');
  const check = parseInt(sin.pop());
  const sum = sin
   .map(multiplyEveryOtherBy2)
    //To individual digits
   .join('').split('')
   .reduce(sumValues,0)
   * 9  % 10
  return check === sum;
}