Add event emitter to datasource

Reviewed By: LukeDefeo

Differential Revision: D51026560

fbshipit-source-id: 8348c6765633d7eecf0d1c80bc5bbd5af8130298

desktop/flipper-plugin-core/src/data-source/DataSource.tsx

@@ -11,6 +11,7 @@ import sortedIndexBy from 'lodash/sortedIndexBy';
 import sortedLastIndexBy from 'lodash/sortedLastIndexBy';
 import property from 'lodash/property';
 import lodashSort from 'lodash/sortBy';
+import EventEmitter from 'eventemitter3';
 
 // If the dataSource becomes to large, after how many records will we start to drop items?
 const dropFactor = 0.1;
@@ -180,6 +181,8 @@ export class DataSource<T extends any, KeyType = never> {
     [viewId: string]: DataSourceView<T, KeyType>;
   };
 
+  public readonly outputEventEmitter = new EventEmitter();
+
   constructor(
     keyAttribute: keyof T | undefined,
     secondaryIndices: IndexDefinition<T>[] = [],
@@ -550,6 +553,7 @@ export class DataSource<T extends any, KeyType = never> {
     Object.entries(this.additionalViews).forEach(([, dataView]) => {
       dataView.processEvent(event);
     });
+    this.outputEventEmitter.emit(event.type, event);
   }
 
   private storeSecondaryIndices(value: T) {