diff --git a/Maths/MobiusFunction.js b/Maths/MobiusFunction.js
index bd268b8bbd..4239d6ab31 100644
--- a/Maths/MobiusFunction.js
+++ b/Maths/MobiusFunction.js
@@ -28,6 +28,6 @@ export const mobiusFunction = (number) => {
   return primeFactorsArray.length !== new Set(primeFactorsArray).size
     ? 0
     : primeFactorsArray.length % 2 === 0
-    ? 1
-    : -1
+      ? 1
+      : -1
 }
diff --git a/Maths/RowEchelon.js b/Maths/RowEchelon.js
index c773bb80a9..cd0db4fc73 100644
--- a/Maths/RowEchelon.js
+++ b/Maths/RowEchelon.js
@@ -117,7 +117,7 @@ const rowEchelon = (matrix) => {
   let result = matrix
 
   // Iterate through the rows (i) and columns (j) of the matrix.
-  for (let i = 0, j = 0; i < numRows && j < numCols; ) {
+  for (let i = 0, j = 0; i < numRows && j < numCols;) {
     // If the current column has all zero elements below the current row,
     // move to the next column.
     if (!checkNonZero(i, j, result)) {
diff --git a/Project-Euler/Problem013.js b/Project-Euler/Problem013.js
index 8748a8ee17..a8b0418058 100644
--- a/Project-Euler/Problem013.js
+++ b/Project-Euler/Problem013.js
@@ -13,7 +13,7 @@ export function largeSum(bignum) {
   let num = 0
 
   while (pos--) {
-    for (let i = nums.length; i--; ) {
+    for (let i = nums.length; i--;) {
       num += +nums[i].charAt(pos)
     }
     ret = (num % 10) + ret
diff --git a/String/GenerateGUID.js b/String/GenerateGUID.js
index 1583920261..eb8d224cd0 100644
--- a/String/GenerateGUID.js
+++ b/String/GenerateGUID.js
@@ -8,7 +8,7 @@ export const Guid = () => {
   const pattern = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'
   let currentDateMilliseconds = new Date().getTime()
   return pattern.replace(/[xy]/g, (currentChar) => {
-    const randomChar = (currentDateMilliseconds + Math.random() * 16) % 16 | 0
+    const randomChar = ((currentDateMilliseconds + Math.random() * 16) % 16) | 0
     currentDateMilliseconds = Math.floor(currentDateMilliseconds / 16)
     return (
       currentChar === 'x' ? randomChar : (randomChar & 0x7) | 0x8
diff --git a/factorial.js b/factorial.js
new file mode 100644
index 0000000000..da06e19766
--- /dev/null
+++ b/factorial.js
@@ -0,0 +1,16 @@
+// 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