onEvent prop for expression component (#64995) (#65043)

* feat: 🎸 add onEvent prop to expression component

* feat: 🎸 add type safety to onEvent prop in expression component

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

src/plugins/expressions/public/index.ts

@@ -37,7 +37,7 @@ export {
   ReactExpressionRendererProps,
   ReactExpressionRendererType,
 } from './react_expression_renderer';
-export { ExpressionRenderHandler } from './render';
+export { ExpressionRenderHandler, ExpressionRendererEvent } from './render';
 export {
   AnyExpressionFunctionDefinition,
   AnyExpressionTypeDefinition,

src/plugins/expressions/public/react_expression_renderer.test.tsx

@@ -26,6 +26,7 @@ import { ExpressionLoader } from './loader';
 import { mount } from 'enzyme';
 import { EuiProgress } from '@elastic/eui';
 import { RenderErrorHandlerFnType } from './types';
+import { ExpressionRendererEvent } from './render';
 
 jest.mock('./loader', () => {
   return {
@@ -135,4 +136,44 @@ describe('ExpressionRenderer', () => {
     expect(instance.find(EuiProgress)).toHaveLength(0);
     expect(instance.find('[data-test-subj="custom-error"]')).toHaveLength(0);
   });
+
+  it('should fire onEvent prop on every events$ observable emission in loader', () => {
+    const dataSubject = new Subject();
+    const data$ = dataSubject.asObservable().pipe(share());
+    const renderSubject = new Subject();
+    const render$ = renderSubject.asObservable().pipe(share());
+    const loadingSubject = new Subject();
+    const loading$ = loadingSubject.asObservable().pipe(share());
+    const eventsSubject = new Subject<ExpressionRendererEvent>();
+    const events$ = eventsSubject.asObservable().pipe(share());
+
+    const onEvent = jest.fn();
+    const event: ExpressionRendererEvent = {
+      name: 'foo',
+      data: {
+        bar: 'baz',
+      },
+    };
+
+    (ExpressionLoader as jest.Mock).mockImplementation(() => {
+      return {
+        render$,
+        data$,
+        loading$,
+        events$,
+        update: jest.fn(),
+      };
+    });
+
+    mount(<ReactExpressionRenderer expression="" onEvent={onEvent} />);
+
+    expect(onEvent).toHaveBeenCalledTimes(0);
+
+    act(() => {
+      eventsSubject.next(event);
+    });
+
+    expect(onEvent).toHaveBeenCalledTimes(1);
+    expect(onEvent.mock.calls[0][0]).toBe(event);
+  });
 });

src/plugins/expressions/public/react_expression_renderer.tsx

@@ -27,6 +27,7 @@ import theme from '@elastic/eui/dist/eui_theme_light.json';
 import { IExpressionLoaderParams, RenderError } from './types';
 import { ExpressionAstExpression, IInterpreterRenderHandlers } from '../common';
 import { ExpressionLoader } from './loader';
+import { ExpressionRendererEvent } from './render';
 
 // Accept all options of the runner as props except for the
 // dom element which is provided by the component itself
@@ -36,6 +37,7 @@ export interface ReactExpressionRendererProps extends IExpressionLoaderParams {
   expression: string | ExpressionAstExpression;
   renderError?: (error?: string | null) => React.ReactElement | React.ReactElement[];
   padding?: 'xs' | 's' | 'm' | 'l' | 'xl';
+  onEvent?: (event: ExpressionRendererEvent) => void;
 }
 
 export type ReactExpressionRendererType = React.ComponentType<ReactExpressionRendererProps>;
@@ -60,6 +62,7 @@ export const ReactExpressionRenderer = ({
   padding,
   renderError,
   expression,
+  onEvent,
   ...expressionLoaderOptions
 }: ReactExpressionRendererProps) => {
   const mountpoint: React.MutableRefObject<null | HTMLDivElement> = useRef(null);
@@ -99,6 +102,13 @@ export const ReactExpressionRenderer = ({
           }
         : expressionLoaderOptions.onRenderError,
     });
+    if (onEvent) {
+      subs.push(
+        expressionLoaderRef.current.events$.subscribe(event => {
+          onEvent(event);
+        })
+      );
+    }
     subs.push(
       expressionLoaderRef.current.loading$.subscribe(() => {
         hasHandledErrorRef.current = false;
@@ -123,7 +133,7 @@ export const ReactExpressionRenderer = ({
 
       errorRenderHandlerRef.current = null;
     };
-  }, [hasCustomRenderErrorHandler]);
+  }, [hasCustomRenderErrorHandler, onEvent]);
 
   // Re-fetch data automatically when the inputs change
   useShallowCompareEffect(

src/plugins/expressions/public/render.ts

@@ -32,7 +32,7 @@ export interface ExpressionRenderHandlerParams {
   onRenderError: RenderErrorHandlerFnType;
 }
 
-interface Event {
+export interface ExpressionRendererEvent {
   name: string;
   data: any;
 }
@@ -45,7 +45,7 @@ interface UpdateValue {
 export class ExpressionRenderHandler {
   render$: Observable<number>;
   update$: Observable<UpdateValue | null>;
-  events$: Observable<Event>;
+  events$: Observable<ExpressionRendererEvent>;
 
   private element: HTMLElement;
   private destroyFn?: any;
@@ -63,7 +63,7 @@ export class ExpressionRenderHandler {
     this.element = element;
 
     this.eventsSubject = new Rx.Subject();
-    this.events$ = this.eventsSubject.asObservable() as Observable<Event>;
+    this.events$ = this.eventsSubject.asObservable() as Observable<ExpressionRendererEvent>;
 
     this.onRenderError = onRenderError || defaultRenderErrorHandler;