4 ways to add the digits of a number in JavaScript

JavaScript program to add the digits of a number:

In this post, I will show you how to write a JavaScript program to add the digits of a given number or it will find the sum of the digits of a number. For example, if the number is 234, it will print 9.

Method 1: Find the sum of digits of a number by using a while loop:

With this approach, we will use one while loop to find the sum. It will follow the following steps:

• Initialize one variable sum as 0 to hold the final sum.
• Run one while loop until the number is greater than 0.
• In the loop, get the rightmost digit of the number and add it to the sum variable.
• At the end of each iteration, remove the rightmost digit from the number.

The loop will stop once all the digits are removed from the number or the number become 0.

The following program shows how to write it in JavaScript:

let n = 234;
let sum = 0;

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

console.log(`Sum: ${sum}`);

• The number is assigned to the variable n. The sum variable is initialized to 0.
• It uses the modulo operator, %, to get the rightmost digit of the number. The operation n % 10 returns the remainder of the division operation n / 10 or the rightmost digit of the number n.
• Math.floor(n/10) removes the rightmost digit of n. The value of n is updated by this value at the end of each loop iteration.

If you run this program, it will print 9.

The above example will update the value of n to 0. We can initialize one new variable before the loop starts:

let n = 234;
let sum = 0;

let no = n;
while(no){
    sum += no % 10;
    no = Math.floor(no/10);
}

console.log(`Sum of digits of ${n}: ${sum}`);

Download it on GitHub

It created a new variable no before the while loop starts. If you run this program, it will not modify the value of n:

Sum of digits of 234: 9

Method 2: By using a for loop:

We can use the same approach with a for loop to find the sum. The syntax of for loop is:

for(initialize, condition, update){
 // body   
}

• The first step initialize runs once. This is used to initialize a variable.
• The second step condition checks for a condition. The loop will run until it is True.
• The third step update runs at the end of each iteration. This is used mainly to update a variable.

The body of the loop runs until the condition is True. We can use a for loop to find the sum of all digits of a number as shown below:

let n = 679;
let sum = 0;

for(let no = n; no > 0; no = Math.floor(no/10)){
    sum += no % 10;
}

console.log(`Sum of digits of ${n}: ${sum}`);

Download it on GitHub

• It initializes the variable no as n when the loop starts.
• At the end of each iteration of the loop, it assigns Math.floor(no/10) to the variable no i.e. it removes the last digit of the number.
• The loop runs until the value of no is greater than 0.
• In the body of the loop, it adds the last digit of no to the sum variable.

It will print the below result:

Sum of digits of 679: 22

Method 3: By converting the number to String:

The number can be converted to a String and we can find the digits by iterating over the characters of the string. The following example shows how it works:

let n = 679;
let sum = 0;

String(n).split('').forEach(e => sum += Number(e));

console.log(`Sum of digits of ${n}: ${sum}`);

Download it on GitHub

• It uses the String() constructor to convert the number n to String.
• It use the split() method to split the string to an array of digits. For example, for the number 679, it will return the array ['6', '7', '9'].
• The forEach loop iterates over the characters of the array. It converts the characters to a number with the Number() constructor and adds it to the sum variable.

Method 4: By using the reduce() function:

The reduce() function is an array operation. It uses a reducer function on each element of the array and calculates a final result. We can use these function to find the sum of all digits of a number.

let n = 679;

let initialValue = 0;
let sum = String(n).split('').reduce((accumulator, currentValue) => accumulator + Number(currentValue), initialValue);

console.log(`Sum of digits of ${n}: ${sum}`);

Download it on GitHub

• The number n is converted to a String and with the split() method we get an array of characters.
• The reduce function takes the second parameter initialValue as the starting value of the accumulator.
• On each step, it converts the current character to number and adds it to the current value of the accumulator. This value is passed as the accumulator value on next call.

It will return the sum of all digits of the number n.

If you run the program, it will print:

Sum of digits of 679: 22

You might also like:

• JavaScript replace multiple characters using single replace call
• How to find simple interest with JavaScript
• Show hide a div in JavaScript on button click
• JavaScript program to check if an element is present in an Array or not
• How to find all matches in an array of objects in JavaScript
• 6 ways in JavaScript to iterate over an array of objects