# JavaScript: Calculate the falling factorial of a number

## JavaScript Math: Exercise-48 with Solution

Write a JavaScript function to calculate the falling factorial of a number.

Let x be a real number (but usually an integer).

Let k be a positive integer.

Then x to the (power of) k falling is:

This is called the kth falling factorial power of x.

**Sample Solution:**

**JavaScript Code:**

```
// Define a function named fallingFactorial that calculates the falling factorial of 'n' to 'k'.
function fallingFactorial(n, k)
{
// Initialize variables 'i' and 'r'.
var i = (n - k + 1),
r = 1;
// Check if 'n' is negative.
if (n < 0)
{
throw new Error("n must be positive.");
}
// Check if 'k' is greater than 'n'.
if (k > n)
{
throw new Error("k cannot be greater than n.");
}
// Implement the falling factorial calculation.
while (i <= n)
{
r *= i++;
}
// Return the result of the falling factorial.
return r;
}
// Output the result of falling factorial calculation with inputs 10 and 2.
console.log(fallingFactorial(10, 2));
```

Output:

90

**Flowchart: **

**Live Demo: **

See the Pen javascript-math-exercise-48 by w3resource (@w3resource) on CodePen.

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