Convert emitters to promise (https://github.com/woocommerce/woocommerce-blocks/pull/2003)

* restructure event-emit directory and convert emitters to promises

- also add emitEventWithAbort function

* implement event emitters as promises

* clean up logic

- return from for loop
- define response as const on each iteration.
- return true if loop completes successfully.

* rename event_emit folder to event-emit

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/checkout/event-emit.js

@@ -1,7 +1,7 @@
 /**
  * Internal dependencies
  */
-import { actions, reducer, emitEvent } from '../event_emit';
+import { actions, reducer, emitEvent, emitEventWithAbort } from '../event-emit';
 
 const EMIT_TYPES = {
 	CHECKOUT_COMPLETE_WITH_SUCCESS: 'checkout_complete',
@@ -70,4 +70,10 @@ const emitterSubscribers = ( dispatcher ) => ( {
 	},
 } );
 
-export { EMIT_TYPES, emitterSubscribers, reducer, emitEvent };
+export {
+	EMIT_TYPES,
+	emitterSubscribers,
+	reducer,
+	emitEvent,
+	emitEventWithAbort,
+};

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/checkout/index.js

@@ -10,6 +10,7 @@ import {
 	EMIT_TYPES,
 	emitterSubscribers,
 	emitEvent,
+	emitEventWithAbort,
 	reducer as emitReducer,
 } from './event-emit';
 
@@ -124,23 +125,18 @@ export const CheckoutProvider = ( {
 	useEffect( () => {
 		const status = checkoutState.status;
 		if ( status === STATUS.PROCESSING ) {
-			const error = emitEvent(
+			emitEventWithAbort(
 				currentObservers.current,
 				EMIT_TYPES.CHECKOUT_PROCESSING,
 				{}
-			);
+			).then( ( response ) => {
-			//@todo bail if error object detected (see flow).
+				if ( response !== true ) {
-			//Fire off checkoutFail event, and then reset checkout
+					// @todo handle any validation error property values in the
-			//status to idle (with hasError flag) - then return from this hook.
+					// response
-			// Finally after the event subscribers have processed, do the
+					dispatchActions.setHasError();
-			// checkout submit sending the order to the server for processing
+				}
-			// and followup on errors from it.
+				dispatch( actions.setComplete() );
-			// I'll need to setup a special emitter that aborts on first fail
+			} );
-			// instead of hitting all subscribed event observers.
-			if ( error ) {
-				dispatchActions.setHasError();
-			}
-			dispatch( actions.setComplete() );
 		}
 		if ( checkoutState.isComplete ) {
 			if ( checkoutState.hasError ) {
@@ -154,14 +150,21 @@ export const CheckoutProvider = ( {
 					currentObservers.current,
 					EMIT_TYPES.CHECKOUT_COMPLETE_WITH_SUCCESS,
 					{}
-				);
+				).then( () => {
-			}
+					// all observers have done their thing so let's redirect
-			// all observers have done their thing so let's redirect (if no error)
+					// (if no error)
-			if ( ! checkoutState.hasError ) {
+					if ( ! checkoutState.hasError ) {
-				window.location = checkoutState.redirectUrl;
+						window.location = checkoutState.redirectUrl;
+					}
+				} );
 			}
 		}
-	}, [ checkoutState.status, checkoutState.hasError ] );
+	}, [
+		checkoutState.status,
+		checkoutState.hasError,
+		checkoutState.isComplete,
+		checkoutState.redirectUrl,
+	] );
 
 	const onSubmit = () => {
 		dispatch( actions.setProcessing() );

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/event-emit/emitters.js

@@ -0,0 +1,63 @@
+/**
+ * Emits events on registered observers for the provided type and passes along
+ * the provided data.
+ *
+ * This event emitter will silently catch promise errors, but doesn't care
+ * otherwise if any errors are caused by observers. So events that do care
+ * should use `emitEventWithAbort` instead.
+ *
+ * @param {Object} observers The registered observers to omit to.
+ * @param {string} eventType The event type being emitted.
+ * @param {*}      data      Data passed along to the observer when it is
+ *                           invoked.
+ *
+ * @return {Promise} A promise that resolves to true after all observers have
+ *                   executed.
+ */
+export const emitEvent = async ( observers, eventType, data ) => {
+	const observersByType = observers[ eventType ] || [];
+	for ( let i = 0; i < observersByType.length; i++ ) {
+		try {
+			await Promise.resolve( observersByType[ i ]( data ) );
+		} catch ( e ) {
+			// we don't care about errors blocking execution, but will
+			// console.error for troubleshooting.
+			// eslint-disable-next-line no-console
+			console.error( e );
+		}
+	}
+	return true;
+};
+
+/**
+ * Emits events on registered observers for the provided type and passes along
+ * the provided data. This event emitter will abort and return any value from
+ * observers that do not return true.
+ *
+ * @param {Object} observers The registered observers to omit to.
+ * @param {string} eventType The event type being emitted.
+ * @param {*}      data      Data passed along to the observer when it is
+ *                           invoked.
+ *
+ * @return {Promise} Returns a promise that resolves to either boolean or the
+ *                   return value of the aborted observer.
+ */
+export const emitEventWithAbort = async ( observers, eventType, data ) => {
+	const observersByType = observers[ eventType ] || [];
+	for ( let i = 0; i < observersByType.length; i++ ) {
+		try {
+			const response = await Promise.resolve(
+				observersByType[ i ]( data )
+			);
+			if ( response !== true ) {
+				return response;
+			}
+		} catch ( e ) {
+			// we don't handle thrown errors but just console.log for
+			// troubleshooting
+			// eslint-disable-next-line no-console
+			console.error( e );
+		}
+	}
+	return true;
+};

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/event-emit/index.js

@@ -0,0 +1,2 @@
+export * from './reducer';
+export * from './emitters';

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/event-emit/reducer.js

@@ -26,26 +26,6 @@ export const actions = {
 	},
 };
 
-/**
- * Emits events on registered observers for the provided type and passes along
- * the provided data.
- *
- * @param {Object} observers The registered observers to omit to.
- * @param {string} eventType The event type being emitted.
- * @param {*}      data      Data passed along to the observer when it is
- *                           invoked.
- */
-export const emitEvent = ( observers, eventType, data ) => {
-	const observersByType = observers[ eventType ] || [];
-	let hasError = false;
-	observersByType.forEach( ( observer ) => {
-		if ( typeof observer === 'function' ) {
-			hasError = !! observer( data, hasError );
-		}
-	} );
-	return hasError;
-};
-
 /**
  * Handles actions for emmitters
  *

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/event-emit/test/emitters.js

@@ -0,0 +1,49 @@
+/**
+ * Internal dependencies
+ */
+import { emitEvent, emitEventWithAbort } from '../emitters';
+
+describe( 'Testing emitters', () => {
+	let observerMocks = {};
+	beforeEach( () => {
+		observerMocks = {
+			observerA: jest.fn().mockReturnValue( true ),
+			observerB: jest.fn().mockReturnValue( true ),
+			observerReturnValue: jest.fn().mockReturnValue( 10 ),
+			observerPromiseWithReject: jest
+				.fn()
+				.mockRejectedValue( 'an error' ),
+			observerPromiseWithResolvedValue: jest.fn().mockResolvedValue( 10 ),
+		};
+	} );
+	describe( 'Testing emitEvent()', () => {
+		it( 'invokes all observers', async () => {
+			const observers = { test: Object.values( observerMocks ) };
+			const response = await emitEvent( observers, 'test', 'foo' );
+			expect( console ).toHaveErroredWith( 'an error' );
+			expect( observerMocks.observerA ).toHaveBeenCalledTimes( 1 );
+			expect( observerMocks.observerB ).toHaveBeenCalledWith( 'foo' );
+			expect( response ).toBe( true );
+		} );
+	} );
+	describe( 'Testing emitEventWithAbort()', () => {
+		it(
+			'aborts on non truthy value and does not invoke remaining ' +
+				'observers',
+			async () => {
+				const observers = { test: Object.values( observerMocks ) };
+				const response = await emitEventWithAbort(
+					observers,
+					'test',
+					'foo'
+				);
+				expect( console ).not.toHaveErrored();
+				expect( observerMocks.observerB ).toHaveBeenCalledTimes( 1 );
+				expect(
+					observerMocks.observerPromiseWithResolvedValue
+				).not.toHaveBeenCalled();
+				expect( response ).toBe( 10 );
+			}
+		);
+	} );
+} );

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/event_emit/index.js

@@ -1 +0,0 @@
-export * from './reducer';

plugins/woocommerce-blocks/assets/js/base/context/cart-checkout/shipping/event-emit.js

@@ -1,7 +1,7 @@
 /**
  * Internal dependencies
  */
-import { actions, reducer, emitEvent } from '../event_emit';
+import { actions, reducer, emitEvent } from '../event-emit';
 
 const EMIT_TYPES = {
 	SHIPPING_RATES_SUCCESS: 'shipping_rates_success',