Dfyjkt

var mul = 1;
 var firstNumber = 0;
 var secondNUmber = 0;
 var firstNumberStr = '';
 var secondNUmberStr = '';

 // prompt user to enter two numbers
 firstNumberStr = prompt("Enter first number: ");

 while(isNaN(firstNumberStr))
 firstNumberStr = prompt("Enter Correct first number: ");
 

 secondNUmberStr = prompt("Enter a number bigger than first number: ");

 while(isNaN(secondNUmberStr) || parseInt(firstNumberStr) >= parseInt(secondNUmberStr))
 secondNUmberStr = prompt("Enter a number bigger than first number: ");
 

 firstNumber = parseInt(firstNumberStr); 
 secondNUmber = parseInt(secondNUmberStr);
 
 for(;firstNumber <= secondNUmber;)
 mul *= firstNumber;
 firstNumber++ 
 
 
 alert(mul);

// declare variables
var number1;
var number2;
var multiply;
var middlePoint;
const INITIAL_VALUE = 0;
// initialize sum
multiply = INITIAL_VALUE;

// prompt user to enter two numbers
number1 = prompt("Enter first number: ");
number2 = prompt("Enter a number bigger than first number: ");

// convert user input into numbers
number1 = Number(number1);
number2 = Number(number2);

// assign middlePoint
middlePoint = number1;

// display number1
document.write(number1);

// assign multiply and increment middlePoint
multiply = middlePoint;
middlePoint++;

// while loop to display numbers in between and multiply
for (var i=0;middlePoint < number2; i++) 
 document.write(" * " + middlePoint);
 multiply *= middlePoint;
 middlePoint++;


// add multiply to number2 for final multiplication total
multiply *= number2;

// display number2 and final multiplication total
document.write(" * " + number2 + " = " + multiply);

let number1, number2, result, resultText;

// prompt user to enter two numbers
number1 = prompt('Enter first number: ');
number2 = prompt('Enter a number bigger than first number: ');

// convert user input into numbers
number1 = Number(number1);
number2 = Number(number2);

// Initialize result and resultText
result = number1;
resultText = '' + number1; 

// for loop to display numbers in between and multiply
for (let i = 1; i <= number2 - number1; i++) 
 const temp = number1 + i;
 result *= temp;
 resultText += ' * ' + temp;


// display final multiplication total
resultText += ' = ' + result;
document.write(resultText);

var num1 = 10;
var num2 = 20;
var product = 1;

document.write(num1);
num1 ++; 

for (;num1 <= num2;) 
 document.write(" * " + num1);
 product *= num1;
 num1++;


// display final product
document.write(" = " + product);