loaded event when loaded from persistence adapter

src/Y.js

@@ -21,9 +21,12 @@ import { addStruct as addType } from './Util/structReferences.js'
 import debug from 'debug'
 import Transaction from './Transaction.js'
 
+import YIndexedDB from '../../y-indexeddb/src/y-indexeddb.js'
+
 export default class Y extends NamedEventHandler {
   constructor (opts, persistence) {
     super()
+    this._loaded = false
     this._opts = opts
     this.userID = opts._userID != null ? opts._userID : generateUserID()
     this.share = {}
@@ -47,6 +50,15 @@ export default class Y extends NamedEventHandler {
       initConnection()
     }
   }
+  get loaded () {
+    return this._loaded
+  }
+  set loaded (val) {
+    if (this._loaded === false && val) {
+      this._loaded = true
+      this.emit('loaded')
+    }
+  }
   _beforeChange () {}
   transact (f, remote = false) {
     let initialCall = this._transaction === null