In this post, we will learn **how to find the factorial of a number using JavaScript** Programming language.

**Factorial **of a number is a function that multiplies every natural number less than that number. For example: **Factorial of 3** is 3 x 2 x 1 = **6**.

We will compute the factorial using a simple for loop function.

So, without further ado, let’s begin this tutorial.

**JavaScript Program to Find Factorial of a Number**

// JavaScript Program to Find Factorial of a Number var num = parseInt(prompt("Enter a positive integer: ")); // Checking if number is negative if (num < 0){ console.log("Factorial of negative numbers doesn't exist."); } // Checking whether number equals to zero else if (num == 0){ console.log("Factorial of 0 is: 1"); } // Checking if number is positive else{ let fact = 1; for (i = 1; i <= num; ++i){ fact = fact * i; } console.log(`Factorial of ${num} is: ${fact}.`); }

**Output 1**

```
Enter a positive integer: -5
Factorial of negative numbers doesn't exist.
```

**Output 2**

```
Enter a positive integer: 0
Factorial of 0 is: 1
```

**Output 3**

```
Enter a positive integer: 4
Factorial of 4 is: 24.
```

**How Does This Program Work ?**

var num = parseInt(prompt("Enter a positive integer: "));

The user is asked to enter a positive integer.

// Checking if number is negative if (num < 0){ console.log("Factorial of negative numbers doesn't exist."); }

If the entered number is less than **0**, we display a message stating that the factorial of negative numbers doesn’t exist.

// Checking whether number equals to zero else if (num == 0){ console.log("Factorial of 0 is: 1");

If the entered number is **0**, then it’s factorial will be** 1**.

// Checking if number is positive else{ let fact = 1; for (i = 1; i <= num; ++i){ fact = fact * i; } console.log(`Factorial of ${num} is: ${fact}.`); }

Now, we calculate the factorial of the positive integer using a** for loop**. The factorial gets stored in the **fact** named variable and is displayed on the screen using the **console.log()** statement.

**Conclusion**

I hope after going through this post, you understand **how to find the factorial of a number using JavaScript **Programming language.

If you have any doubt regarding the program, feel free to contact us in the comment section. We will be delighted to help you.

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