fixed YArray

src/utils/Snapshot.js

@@ -0,0 +1,23 @@
+import { DeleteSet, isDeleted } from './DeleteSet'
+import { AbstractItem } from '../structs/AbstractItem.js' // eslint-disable-line
+
+export class Snapshot {
+  /**
+   * @param {DeleteSet} ds delete store
+   * @param {Map<number,number>} sm state map
+   * @param {Map<number,string>} userMap
+   */
+  constructor (ds, sm, userMap) {
+    this.ds = new DeleteSet()
+    this.sm = sm
+    this.userMap = userMap
+  }
+}
+
+/**
+ * @param {AbstractItem} item
+ * @param {Snapshot} [snapshot]
+ */
+export const isVisible = (item, snapshot) => snapshot === undefined ? !item._deleted : (
+  snapshot.sm.has(item.id.client) && (snapshot.sm.get(item.id.client) || 0) > item.id.clock && !isDeleted(snapshot.ds, item._id)
+)