--description--

Given a string, determine if it's a valid ISBN-10.

An ISBN-10 consists of hyphens ("-") and 10 other characters. After removing the hyphens ("-"):

• The first 9 characters must be digits, and
• The final character may be a digit or the letter "X", which represents the number 10.

To validate it:

• Multiply each digit (or value) by its position (multiply the first digit by 1, the second by 2, and so on).
• Add all the results together.
• If the total is divisible by 11, it's valid.

--hints--

isValidIsbn10("0-306-40615-2") should return true.

assert.isTrue(isValidIsbn10("0-306-40615-2"));

isValidIsbn10("0-306-40615-1") should return false.

assert.isFalse(isValidIsbn10("0-306-40615-1"));

isValidIsbn10("0-8044-2957-X") should return true.

assert.isTrue(isValidIsbn10("0-8044-2957-X"));

isValidIsbn10("X-306-40615-2") should return false.

assert.isFalse(isValidIsbn10("X-306-40615-2"));

isValidIsbn10("0-6822-2589-4") should return true.

assert.isTrue(isValidIsbn10("0-6822-2589-4"));

--seed--

--seed-contents--

function isValidIsbn10(str) {

  return str;
}

--solutions--

function isValidIsbn10(str) {
  const isbn = str.replace(/-/g, "");

  if (isbn.length !== 10) return false;

  let sum = 0;

  for (let i = 0; i < 9; i++) {
    const digit = Number(isbn[i]);
    if (Number.isNaN(digit)) return false;

    sum += digit * (i + 1);
  }

  const last = isbn[9];

  if (last === "X") {
    sum += 10 * 10;
  } else {
    const digit = Number(last);
    if (Number.isNaN(digit)) return false;

    sum += digit * 10;
  }

  return sum % 11 === 0;
}