JavaScript: Add digits until there is only one digit

/**
 * Function to add the digits of a number until there is only one digit left.
 * @param {number} n - The number to process.
 * @returns {number} - The result of adding digits until only one digit remains.
 */
function test(n) {
  if (isNaN(n) || n === 0) return 0;  // Return 0 if input is not a number or is 0
  total = n; // Initialize total with the input number
    while (n >= 10) {        // Loop until the number becomes a single digit
        total = 0; // Reset total
        while (n != 0) { // Loop to add digits of the number
            total += Math.floor(n % 10); // Add the last digit to total
            n = Math.floor(n / 10); // Remove the last digit
        }
        n = total; // Update n with the new total
    }
    
    return total; // Return the final total
};  
// Test cases
n = 49;
console.log("n = " +n);
console.log("Add digits of the said number until there is only one digit: "+test(n));

n = 9;
console.log("Original text: " +n);
console.log("Add digits of the said number until there is only one digit: "+test(n));

/**
 * Function to add the digits of a number until there is only one digit left.
 * @param {number} n - The number to process.
 * @returns {number} - The result of adding digits until only one digit remains.
 */
function test(n) {
    if (isNaN(n) || n === 0) return 0; // Return 0 if input is not a number or is 0
    if (n < 10) return n; // Return the number itself if it is already a single digit
    return n % 9 === 0 ? 9 : n % 9; // If n is divisible by 9, return 9; otherwise, return the remainder of n divided by 9
};

// Test cases
n = 49;
console.log("n = " +n);
console.log("Add digits of the said number until there is only one digit: "+test(n));

n = 9;
console.log("Original text: " +n);
console.log("Add digits of the said number until there is only one digit: "+test(n));