 # JavaScript Program to Add Digits of a Number

In this article, you will learn and get code to add digits of a number in JavaScript. Here are the list of JavaScript programs, you will go through:

• Add digits of number in JavaScript without user input
• Allow user to enter the number. Live output of this program is given

## Add Digits of a Number in JavaScript

This program does not allows user to enter the data. That is, this program only adds all the digits of a number say 1234 and prints its addition result on output.

This is just a simple JavaScript code that reminds you, how the addition of all digits of a number gets performed

```<!doctype html>
<html>
<body>
<script>
var num=1234, rem, sum=0;
while(num)
{
rem = num%10;
sum = sum+rem;
num = Math.floor(num/10);
}
document.write(sum);
</script>
</body>
</html>```

Save this code in a file with .html extension and open it in a web browser. Here is the output:

Note - The Math.floor() method rounds the number to its nearest integer. That is, Math.floor(12/10) gives you 1, instead of 1.2

The following code:

```while(num)
{
rem = num%10;
sum = sum+rem;
num = Math.floor(num/10);
}```

works in a way that:

• The condition, of while loop evaluates to be true, because the value of num is not 0, initially
• So program flow goes inside the loop
• There num%10 or 1234%10 or 4 gets initialized to rem. So rem=4
• And sum+rem or 0+4 or 4 gets initialized to sum. So sum=4
• The final statement, Math.floor(num/10) or Math.floor(1234/10) or Math.floor(123.4) or 123 gets initialized to num
• Now again the condition of while loop gets evaluated. Because the value of num is 123 which is not equal to 0, therefore again the condition evaluates to be true
• So program flow again goes inside the loop and evaluates all the three statements
• This process continues until the condition of while loop evaluates to be false

The document.write() method writes the value of sum into an HTML output.

### Get Input from User

This program allows user to enter the number, then find and prints the sum of digits of that entered (given) number as shown here:

```<!doctype html>
<html>
<script>
{
var num, rem, sum=0;
num = parseInt(document.getElementById("num").value);
while(num)
{
rem = num%10;
sum = sum+rem;
num = Math.floor(num/10);
}
document.getElementById("result").value = sum;
}
</script>
<body>
<p>Enter the Number: <input id="num"></p>
<p>Result = <input id="result"></p>
</body>
</html>```

Here is its sample output with user input, 1234:

#### Live Output of Previous Program

Here is the live output of above JavaScript program on addition of digits of given number by user:

Enter the Number:

Result =

After clicking on the button named Add Digits of Number, a function addDigitsOfNumber() gets called. Therefore, all the statements inside this function gets executed, and the value of input whose id is result gets changed with the value of sum.