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# Factorial of a number using JavaScript

Given a positive integer n and the task is to find the factorial of that number using JavaScript code.

For any positive integer ‘n’, the factorial of n is the product of all the values from 1 to n. In mathematics factorial of n is represented by n!. Factorial of 0 is 1.

Note: Factorials of negative numbers are not defined as only positive numbers including 0 are defined in the domain of factorials.

JavaScript Program for Factorial

Examples:

Input : 4
Output : 24

Input : 5
Output : 120

## Approach 1: Iterative Method

• Declare a variable with a value of the number whose factorial you have to find.
• Declare a function factorial taking the value as a parameter.
• In the function definition, initialize variable ans to 1.
• Loop in the range of [2, n].
• Multiply ans by the value of i in each iteration.
• Return the value of ans.

Example:

## Javascript

 let n = 5;   function factorial(n) {     let ans = 1;           if(n === 0)        return 1;    for (let i = 2; i <= n; i++)         ans = ans * i;     return ans; }  console.log(factorial(n));

Output

120


Since the code is running for all the values of n, Time Complexity: O(n):

As we are not allocating any extra space for a variable so the Auxiliary Space: O(1):

## Approach 2: Recursive Method

• Declare a variable with a value of the number whose factorial you have to find.
• Declare a recursive function factorial taking the value as a parameter.
• The function returns 1 if the value is 0 else the return calls the function for value – 1.
• After recursion is over the value returned is the factorial.

Example:

## Javascript

 let n = 5;function factorial(n) {     if (n === 0) {         return 1;     }     else {         return n * factorial( n - 1 );     } }   console.log(factorial(n));

Output

120

Since the code is running for all the values of n, Time Complexity: O(n)

As the stack is being created for each function call, so Auxiliary Space: O(n)