In this article, we will learn how to find the sum of digits of a given number. The sum of digits can be obtained by adding each number from a given integer. There are many ways to find the sum of the digits of a number. We will see some of the approaches –

Table of Contents

• Using for loop
• Using for loop with string conversion
• Using Array.reduce method
• Using recursion

Using for loop

You can use a for loop to manually extract each number using modulo (%) and division (/).

function sumOfDigitsForLoop(num) {
  let sum = 0;
  for (let i = num; i > 0; i = Math.floor(i / 10)) {
    sum += i % 10;
  }
  return sum;
}

console.log(sumOfDigitsForLoop(1234)); // Output: 10

Using for loop with string conversion

In this approach, we first convert the number to a string then loop through each character of the string and sum them.

function sumOfDigitsForLoopString(num) {
  let sum = 0;
  const str = num.toString();
  
  for (let i = 0; i < str.length; i++) {
    sum += parseInt(str[i]);
  }

  return sum;
}

console.log(sumOfDigitsForLoopString(1234)); // Output: 10

Using Array.reduce method

In this approach, we first convert the number into string then split them into digits, and finally use reduce to sum them.

function sumOfDigits(num) {
  return num
    .toString()
    .split('')
    .reduce((sum, digit) => sum + parseInt(digit), 0);
}

console.log(sumOfDigits(1234)); // Output: 10

Using recursion

You can use the recursion method where the function keeps calling itself until the number becomes 0.

function sumOfDigits(num) {
  if (num === 0) return 0;
  return (num % 10) + sumOfDigits(Math.floor(num / 10));
}

console.log(sumOfDigits(1234)); // Output: 10