fix: Fix throwing intersectionObserver is not defined error in SSR mode

Author: yanceyy

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-notion-x-code-block",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "description": "",
   "type": "module",
   "module": "dist/index.js",

src/manager.ts

@@ -1,12 +1,17 @@
 type HandlerFunction = (element: Element) => void;
 
 class ObserverManager {
-  private observer: IntersectionObserver;
+  private observer?: IntersectionObserver;
   private handlers: Map<Element, HandlerFunction>;
 
   constructor() {
     this.handlers = new Map();
 
+    // Skip when SSR
+    if (typeof window === "undefined") {
+      return;
+    }
+
     this.observer = new IntersectionObserver(
       (entries) => {
         entries.forEach((entry) => {
@@ -26,14 +31,14 @@ class ObserverManager {
   // Return unobserve callback directly
   observe(element: Element, handler: HandlerFunction): () => void {
     this.handlers.set(element, handler);
-    this.observer.observe(element);
+    this.observer?.observe(element);
 
     return () => this.unobserve(element);
   }
 
   unobserve(element: Element): void {
     this.handlers.delete(element);
-    this.observer.unobserve(element);
+    this.observer?.unobserve(element);
   }
 }