JavaScript Program to Find LCM

In this example, you will learn to write a JavaScript program that finds the LCM of two numbers.

To understand this example, you should have the knowledge of the following JavaScript programming topics:


The Least Common Multiple (LCM) of two integers is the smallest positive integer that is perfectly divisible by both integers.

For example, the LCM of 6 and 8 is 24.


Example 1: LCM Using while Loop and if Statement

// program to find the LCM of two integers

// take input
const num1 = prompt('Enter a first positive integer: ');
const num2 = prompt('Enter a second positive integer: ');

// higher number among number1 and number2 is stored in min
let min = (num1 > num2) ? num1 : num2;

// while loop
while (true) {
    if (min % num1 == 0 && min % num2 == 0) {
        console.log(`The LCM of ${num1} and ${num2} is ${min}`);
        break;
    }
    min++;
}

Output

Enter a first positive integer: 6
Enter a second positive integer: 8
The LCM of 6 and 8 is 24

In the above program, the user is prompted to enter two positive integers.

The greater number among the numbers provided by the user is stored in a min variable. The LCM of two numbers cannot be less than the greater number.

The while loop is used with an if statement. In each iteration,

  • The variable min is divided by both the num1 and num2.
  • If both number's remainder is equal to 0, then it is the LCM and the break statement terminates the program.
  • If both number's remainder is not equal to 0, the value of min is increased by 1 and the loop continues.
  • The while loop continues until the condition is met.
    if (min % num1 == 0 && min % num2 == 0)

The LCM of two numbers can also be found using the formula:

LCM = (num1*num2) / HCF

To learn about how to find the HCF, visit the JavaScript program to find HCF.

Example 2: LCM Calculation Using HCF

// program to find the LCM of two integers

let hcf;
// take input
const number1 = prompt('Enter a first positive integer: ');
const number2 = prompt('Enter a second positive integer: ');

// looping from 1 to number1 and number2 to find HCF
for (let i = 1; i <= number1 && i <= number2; i++) {

    // check if is factor of both integers
    if( number1 % i == 0 && number2 % i == 0) {
        hcf = i;
    }
}

// find LCM
let lcm = (number1 * number2) / hcf;

// display the hcf
console.log(`HCF of ${number1} and ${number2} is ${lcm}.`);

Output

Enter a first positive integer: 6
Enter a second positive integer: 8
The LCM of 6 and 8 is 24.

In the above program, firstly HCF of the numbers is calculated. Then LCM is calculated using the given formula.