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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