Sum all the Digits in a Number using JavaScript

# Sum all the Digits in a Number using JavaScript

To sum all the digits in a number:

1. Convert the number to a string.
2. Use the split() method to split the string into an array of digits.
3. Use the reduce() method to sum up all the digits in the array.

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function getSumOfDigits(num) {
  return String(num)
    .split('')
    .reduce((accumulator, digit) => {
      return accumulator + Number(digit);
    }, 0);
}

console.log(getSumOfDigits(1)); // 👉️ 1
console.log(getSumOfDigits(123)); // 👉️ 6
console.log(getSumOfDigits(1234)); // 👉️ 10

The function takes a number as a parameter and returns the sum of the digits of the number.

We used the String() constructor to convert the number to a string and then used the String.split() method to split the string into an array of digits.

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console.log('1'.split('')); // 👉️ ['1']
console.log('123'.split('')); // 👉️ ['1', '2', '3']
console.log('1234'.split('')); // 👉️ ['1', '2', '3', '4']

We passed an empty string to the String.split() method to split the string on each character (digit).

The last step is to use the Array.reduce() method to iterate over the array.

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function getSumOfDigits(num) {
  return String(num)
    .split('')
    .reduce((accumulator, digit) => {
      return accumulator + Number(digit);
    }, 0);
}

console.log(getSumOfDigits(1)); // 👉️ 1
console.log(getSumOfDigits(123)); // 👉️ 6
console.log(getSumOfDigits(1234)); // 👉️ 10

The function we passed to the reduce() method gets called with each element (digit) in the array.

The second argument we passed to the method is the initial value for the accumulator variable.

On each iteration, we return the sum of the accumulator and the current digit.

Whatever we return from the callback function gets passed as the accumulator on the next iteration.

Once the reduce() method iterates over the entire array, we have the sum of all the digits in the number.

Alternatively, you can use a while loop.

# Sum all the Digits in a Number using a while loop

This is a three-step process:

1. Initialize a sum variable to 0.
2. Use the modulo operator to get each digit of the number.
3. Add each digit to the sum variable.

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function getSumOfDigits(num) {
  let initialNumber = num;
  let sum = 0;

  while (initialNumber) {
    sum += initialNumber % 10;
    initialNumber = Math.floor(initialNumber / 10);
  }

  return sum;
}

console.log(getSumOfDigits(1)); // 👉️ 1
console.log(getSumOfDigits(123)); // 👉️ 6
console.log(getSumOfDigits(1234)); // 👉️ 10

We used a while loop to iterate for as long as the initialNumber variable stores a truthy value (not 0).

On each iteration, we use the modulo % operator to get the remainder of dividing the number by 10.

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console.log(1234 % 10); // 👉️ 4
console.log(123 % 10); // 👉️ 3
console.log(12 % 10); // 👉️ 2

The expression returns the last digit of the number.

The next step is to reassign the initialNumber variable so that the last digit is removed.

On each iteration, we get the last digit of the number and add it to the sum variable.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Get the Sum of all Values in a Map using JavaScript
• How to Sum the Values of an Object in JavaScript
• How to Sum a Property in an Array of Objects in JavaScript
• Get the Sum of an Array of Numbers in JavaScript