add plugin support

storage.js

@@ -27,9 +27,20 @@ class Session {
 export class Storage {
   constructor() {
     this.session = new Session()
+    this.plugins = []
+  }
+
+  addPlugin(plugin) {
+    this.plugins.push(plugin)
   }
 
   getItem(k) {
+    for (const plugin of this.plugins) {
+      const result = plugin(k)
+      if (result ?? undefined !== undefined) {
+        return result
+      }
+    }
     return localStorage.getItem(k)
   }