feat(middleware): accept partial methods (#4673)

* fix(middleware): accept partial methods

* make public api optional, not the internal one

* rename the types

* ensure at least one method is given to a middleware

* fix lint error

Author: Eunjae Lee

src/lib/InstantSearch.ts

@@ -269,7 +269,12 @@ See ${createDocumentationLink({
    */
   public use(...middleware: Middleware[]): this {
     const newMiddlewareList = middleware.map(fn => {
-      const newMiddleware = fn({ instantSearchInstance: this });
+      const newMiddleware = {
+        subscribe: noop,
+        unsubscribe: noop,
+        onStateChange: noop,
+        ...fn({ instantSearchInstance: this }),
+      };
       this.middleware.push({
         creator: fn,
         instance: newMiddleware,

src/lib/__tests__/InstantSearch-test.js

@@ -287,6 +287,20 @@ See documentation: https://www.algolia.com/doc/api-reference/widgets/instantsear
 For more information, visit https://www.algolia.com/doc/guides/getting-insights-and-analytics/search-analytics/click-through-and-conversions/how-to/send-click-and-conversion-events-with-instantsearch/js/`
     );
   });
+
+  it('accepts middleware with partial methods', () => {
+    const search = new InstantSearch({
+      indexName: 'indexName',
+      searchClient: createSearchClient(),
+    });
+
+    const subscribe = jest.fn();
+    search.use(() => ({
+      subscribe,
+    }));
+    search.start();
+    expect(subscribe).toHaveBeenCalledTimes(1);
+  });
 });
 
 describe('InstantSearch', () => {

src/middlewares/createInsightsMiddleware.ts

@@ -1,7 +1,7 @@
 import {
   InsightsClient,
   InsightsClientMethod,
-  Middleware,
+  InternalMiddleware,
   Hit,
 } from '../types';
 import { getInsightsAnonymousUserTokenInternal } from '../helpers';
@@ -30,7 +30,9 @@ export type InsightsProps = {
   ) => void;
 };
 
-export type CreateInsightsMiddleware = (props: InsightsProps) => Middleware;
+export type CreateInsightsMiddleware = (
+  props: InsightsProps
+) => InternalMiddleware;
 
 export const createInsightsMiddleware: CreateInsightsMiddleware = props => {
   const { insightsClient: _insightsClient, insightsInitParams, onEvent } =

src/middlewares/createMetadataMiddleware.ts

@@ -1,4 +1,4 @@
-import { InstantSearch, Middleware, Widget } from '../types';
+import { InstantSearch, InternalMiddleware, Widget } from '../types';
 import { Index } from '../widgets/index/index';
 
 type WidgetMetaData = {
@@ -80,7 +80,7 @@ export function isMetadataEnabled() {
  * - widget name
  * - connector name
  */
-export function createMetadataMiddleware(): Middleware {
+export function createMetadataMiddleware(): InternalMiddleware {
   return ({ instantSearchInstance }) => {
     const payload: Payload = {
       widgets: [],

src/middlewares/createRouterMiddleware.ts

@@ -4,7 +4,7 @@ import {
   Router,
   StateMapping,
   UiState,
-  Middleware,
+  InternalMiddleware,
   RouteState,
 } from '../types';
 import { isEqual } from '../lib/utils';
@@ -14,7 +14,7 @@ export type RouterProps = {
   stateMapping?: StateMapping;
 };
 
-export type RoutingManager = (props?: RouterProps) => Middleware;
+export type RoutingManager = (props?: RouterProps) => InternalMiddleware;
 
 export const createRouterMiddleware: RoutingManager = (props = {}) => {
   const {

src/types/middleware.ts

@@ -1,5 +1,6 @@
 import InstantSearch from '../lib/InstantSearch';
 import { UiState } from './widget';
+import { AtLeastOne } from './utils';
 
 export type MiddlewareDefinition = {
   onStateChange(options: { uiState: UiState }): void;
@@ -11,4 +12,10 @@ export type MiddlewareOptions = {
   instantSearchInstance: InstantSearch;
 };
 
-export type Middleware = (options: MiddlewareOptions) => MiddlewareDefinition;
+export type InternalMiddleware = (
+  options: MiddlewareOptions
+) => MiddlewareDefinition;
+
+export type Middleware = (
+  options: MiddlewareOptions
+) => AtLeastOne<MiddlewareDefinition>;

src/types/utils.ts

@@ -2,3 +2,9 @@ export type HighlightedParts = {
   value: string;
   isHighlighted: boolean;
 };
+
+// https://stackoverflow.com/questions/48230773/how-to-create-a-partial-like-that-requires-a-single-property-to-be-set/48244432#48244432
+export type AtLeastOne<
+  TTarget,
+  TMapped = { [Key in keyof TTarget]: Pick<TTarget, Key> }
+> = Partial<TTarget> & TMapped[keyof TMapped];