don't emit until bootstrapped with data (#47)

client/lib/patch-db.ts

@@ -1,5 +1,13 @@
 import { Bootstrapper, DBCache, Dump, Revision, Update } from './types'
-import { BehaviorSubject, Observable, Subscription, withLatestFrom } from 'rxjs'
+import {
+  BehaviorSubject,
+  filter,
+  Observable,
+  Subscription,
+  switchMap,
+  take,
+  withLatestFrom,
+} from 'rxjs'
 import {
   applyOperation,
   getValueByPointer,
@@ -15,7 +23,10 @@ export class PatchDB<T extends { [key: string]: any }> {
     }
   } = {}
 
-  readonly cache$ = new BehaviorSubject({ sequence: 0, data: {} as T })
+  readonly cache$ = new BehaviorSubject<DBCache<T>>({
+    sequence: 0,
+    data: {} as T,
+  })
 
   constructor(private readonly source$: Observable<Update<T>[]>) {}
 
@@ -118,18 +129,21 @@ export class PatchDB<T extends { [key: string]: any }> {
     >
   >
   watch$(...args: (string | number)[]): Observable<any> {
+    return this.cache$.pipe(
+      filter(({ sequence }) => !!sequence),
+      take(1),
+      switchMap(({ data }) => {
         const path = args.length ? `/${args.join('/')}` : ''
-
         if (!this.watchedNodes[path]) {
-      const data = this.cache$.value.data
           const value = getValueByPointer(data, path)
           this.watchedNodes[path] = {
             subject: new BehaviorSubject(value),
             pathArr: jsonPathToKeyArray(path),
           }
         }
-
         return this.watchedNodes[path].subject
+      }),
+    )
   }
 
   proccessUpdates(updates: Update<T>[], cache: DBCache<T>) {