diff --git a/code_to_optimize_js_esm/fibonacci.js b/code_to_optimize_js_esm/fibonacci.js
index 0ee526315..1a299d4b4 100644
--- a/code_to_optimize_js_esm/fibonacci.js
+++ b/code_to_optimize_js_esm/fibonacci.js
@@ -13,7 +13,17 @@ export function fibonacci(n) {
     if (n <= 1) {
         return n;
     }
-    return fibonacci(n - 1) + fibonacci(n - 2);
+    
+    let prev = 0;
+    let curr = 1;
+    
+    for (let i = 2; i <= n; i++) {
+        const next = prev + curr;
+        prev = curr;
+        curr = next;
+    }
+    
+    return curr;
 }
 
 /**