JavaScript: Find the number of times to replace a given number with the sum of its digits until it convert to a single digit number

JavaScript Basic: Exercise-105 with Solution

Write a JavaScript program to find the number of times to replace a given number with the sum of its digits. This is until it converts to a single-digit number.

Visual Presentation:

Sample Solution:

JavaScript Code:

 // Function to calculate the sum of digits in a number
function digit_to_one(num) {
    // Inner function to compute the sum of digits in a number
    var digitSum = function(num) {
        var digit_sum = 0; // Initialize the variable to store the sum of digits
        while (num) { // Loop to extract digits and sum them
            digit_sum += num % 10; // Add the last digit to the sum
            num = Math.floor(num / 10); // Remove the last digit from the number
        }
        return digit_sum; // Return the sum of digits
    };

    var result = 0; // Initialize the counter for the number of steps

    while (num >= 10) { // Loop until the number becomes a single digit
        result += 1; // Increment the counter for each step
        num = digitSum(num); // Get the sum of digits and assign it to the number
    }

    return result; // Return the count of steps required
}

// Example usage of the function
console.log(digit_to_one(123));  
console.log(digit_to_one(156));  

Output:

1
2

Live Demo:

See the Pen javascript-basic-exercise-105 by w3resource (@w3resource) on CodePen.

Flowchart:

ES6 Version:

// Function to calculate the sum of digits in a number
const digitSum = (num) => {
    let digit_sum = 0; // Initialize sum of digits variable
    while (num) { // Loop to calculate the sum of digits
        digit_sum += num % 10; // Add the last digit to the sum
        num = Math.floor(num / 10); // Remove the last digit from the number
    }	
    return digit_sum; // Return the sum of digits
};

// Function to convert a number to one digit by finding the sum of its digits until it becomes a single digit
const digit_to_one = (num) => {
    let result = 0; // Initialize count of steps to convert number to a single digit
    while (num >= 10) { // Loop until the number becomes a single digit
        result += 1; // Increment the step count
        num = digitSum(num); // Calculate the sum of digits and assign it to the number
    }
    return result; // Return the count of steps taken
};

// Example usage of the function
console.log(digit_to_one(123));
console.log(digit_to_one(156));

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