feat: implement waitFor option

Author: wheresrhys

packages/fetch-mock/src/Route.ts

@@ -31,6 +31,7 @@ export type UserRouteSpecificConfig = {
 	response?: RouteResponse | RouteResponseFunction;
 	repeat?: number;
 	delay?: number;
+	waitFor?: RouteName;
 	sticky?: boolean;
 };
 export type InternalRouteConfig = {
@@ -122,13 +123,15 @@ e.g. {"body": {"status: "registered"}}`);
 class Route {
 	config: RouteConfig;
 	matcher: RouteMatcherFunction;
+	#responseSubscriptions: Array<() => void>;
 
 	constructor(config: RouteConfig) {
 		this.init(config);
 	}
 
 	init(config: RouteConfig | ModifyRouteConfig) {
 		this.config = config;
+		this.#responseSubscriptions = [];
 		this.#sanitize();
 		this.#validate();
 		this.#generateMatcher();
@@ -197,6 +200,21 @@ class Route {
 		}
 	}
 
+	waitFor(awaitedRoute: Route) {
+		const { response } = this.config;
+		this.config.response = () => {
+			return new Promise((res) =>
+				awaitedRoute.onRespond(() => {
+					res(response);
+				}),
+			);
+		};
+	}
+
+	onRespond(func: () => void) {
+		this.#responseSubscriptions.push(func);
+	}
+
 	constructResponse(responseInput: RouteResponseConfig): {
 		response: Response;
 		responseOptions: ResponseInit;
@@ -205,11 +223,15 @@ class Route {
 		const responseOptions = this.constructResponseOptions(responseInput);
 		const body = this.constructResponseBody(responseInput, responseOptions);
 
-		return {
+		const responsePackage = {
 			response: new this.config.Response(body, responseOptions),
 			responseOptions,
 			responseInput,
 		};
+
+		this.#responseSubscriptions.forEach((func) => func());
+
+		return responsePackage;
 	}
 
 	constructResponseOptions(

packages/fetch-mock/src/Router.ts

@@ -342,6 +342,21 @@ export default class Router {
 				'fetch-mock: Adding route with same name as existing route.',
 			);
 		}
+		if (route.config.waitFor) {
+			const routeToAwait = this.routes.find(
+				({ config: { name: existingName } }) =>
+					route.config.waitFor === existingName,
+			);
+
+			if (!routeToAwait) {
+				throw new Error(
+					`Cannot wait for route \`${route.config.waitFor}\`: route of that name does not exist`,
+				);
+			} else {
+				route.waitFor(routeToAwait);
+			}
+		}
+
 		this.routes.push(route);
 	}
 	setFallback(response?: RouteResponse) {

packages/fetch-mock/src/__tests__/FetchMock/response-negotiation.test.js

@@ -119,7 +119,7 @@ describe('response negotiation', () => {
 	describe('waitFor', () => {
 		it('Error informatively if route to wait for does not exist', () => {
 			expect(() => fm.route('*', 200, { waitFor: 'huh' })).toThrow(
-				'no way on your nelly',
+				'Cannot wait for route `huh`: route of that name does not exist',
 			);
 		});
 		it('Not respond until waited for route responds', async () => {