diff --git a/code_to_optimize_js_esm/fibonacci.js b/code_to_optimize_js_esm/fibonacci.js
index 0ee526315..956011bf7 100644
--- a/code_to_optimize_js_esm/fibonacci.js
+++ b/code_to_optimize_js_esm/fibonacci.js
@@ -13,7 +13,14 @@ export function fibonacci(n) {
     if (n <= 1) {
         return n;
     }
-    return fibonacci(n - 1) + fibonacci(n - 2);
+    let a = 0;
+    let b = 1;
+    for (let i = 2; i <= n; i++) {
+        const next = a + b;
+        a = b;
+        b = next;
+    }
+    return b;
 }
 
 /**