update instructions

exercises/02.side-effects/01.problem.effects/README.mdx

@@ -21,7 +21,7 @@ The only way to be notified of a back/forward event is to listen for the
 `popstate` event. You can do this by adding an event listener to the `window`
 object.
 
-```javascript
+```tsx
 window.addEventListener('popstate', () => {
 	// update the input value
 })

exercises/02.side-effects/README.mdx

@@ -4,7 +4,7 @@
 after React renders (and re-renders) your component to the DOM. It accepts a
 callback function which React will call after the DOM has been updated:
 
-```javascript
+```tsx
 useEffect(() => {
 	// your side-effect code here.
 	// this is where you can interact with browser APIs for example