Added factorial function

Author: Sruthi U

factorial.js

@@ -0,0 +1,17 @@
+
+// Function to calculate factorial
+
+function factorial(n) {
+    if (!Number.isInteger(n) || n < 0) {
+        throw new Error("Enter a non-negative integer");
+    }
+
+    if (n === 0 || n === 1) {
+        return 1;
+    }
+
+    return n * factorial(n - 1);
+}
+
+// Example usage
+console.log(factorial(5)); // Output: 120