JavaScript program to find the HCF or GCD of two numbers using the Euclidean algorithm:
let firstNumber = parseInt(prompt("Enter the first number:"));
let secondNumber = parseInt(prompt("Enter the second number:"));
while (secondNumber !== 0) {
let temp = secondNumber;
secondNumber = firstNumber % secondNumber;
firstNumber = temp;
}
console.log("The HCF or GCD of the numbers is: " + firstNumber);