Export EventOrderer type and fix falsy check

src/SlidingWindow.test.ts

@@ -101,15 +101,15 @@ describe('SlidingWindow', () => {
     const onExpire = vi.fn();
     const sliding = new SlidingWindow(1, onExpire);
 
-    const msg2a = createMessage(2);
-    const msg2b = createMessage(2);
+    const msg1a = createMessage(2);
+    const msg1b = createMessage(2);
 
-    sliding.addMessage(msg2a);
-    sliding.addMessage(msg2b);
+    sliding.addMessage(msg1a);
+    sliding.addMessage(msg1b);
 
     await new Promise((resolve) => setTimeout(resolve, 1));
 
     expect(onExpire).toHaveBeenCalledTimes(1);
-    expect(onExpire).toHaveBeenNthCalledWith(1, msg2a);
+    expect(onExpire).toHaveBeenNthCalledWith(1, msg1a);
   });
 });

src/SlidingWindow.ts

@@ -1,12 +1,13 @@
 import { Types as AblyTypes } from 'ably';
+import type { EventOrderer } from './types/mutations';
 
 export default class SlidingWindow {
   private messages: AblyTypes.Message[] = [];
 
   constructor(
     private readonly windowSizeMs: number,
     private onExpire: (message: AblyTypes.Message) => void,
-    private readonly eventOrderer: (a: AblyTypes.Message, b: AblyTypes.Message) => number = defaultOrderLexicoId,
+    private readonly eventOrderer: EventOrderer = defaultOrderLexicoId,
   ) {}
 
   public addMessage(message: AblyTypes.Message) {

src/Stream.ts

@@ -4,6 +4,7 @@ import { Subject, Subscription } from 'rxjs';
 
 import SlidingWindow from './SlidingWindow.js';
 import type { StandardCallback } from './types/callbacks';
+import type { EventOrderer } from './types/mutations.js';
 import EventEmitter from './utilities/EventEmitter.js';
 
 /**
@@ -61,8 +62,6 @@ export type EventBufferOptions = {
   eventOrderer?: EventOrderer;
 };
 
-type EventOrderer = (a: AblyTypes.Message, b: AblyTypes.Message) => number;
-
 /**
  * A state transition emitted as an event from the stream describing a change to the stream's lifecycle.
  */

src/StreamRegistry.ts

@@ -16,7 +16,7 @@ export default class StreamRegistry implements IStreamRegistry {
    * @param {Pick<StreamOptions, 'ably' | 'logger'>} options - The default options used when instantiating a stream.
    */
   constructor(readonly options: Pick<StreamOptions, 'ably' | 'logger' | 'eventBufferOptions'>) {
-    if (options.eventBufferOptions !== null) {
+    if (options.eventBufferOptions) {
       const bufferMs = options.eventBufferOptions?.bufferMs || 0;
       if (bufferMs < 0) {
         throw new Error(`EventBufferOptions bufferMs cannot be less than zero: ${bufferMs}`);

src/types/mutations.ts

@@ -1,3 +1,4 @@
+import { Types as AblyTypes } from 'ably';
 import type { Event } from './model';
 
 /**
@@ -6,6 +7,13 @@ import type { Event } from './model';
  */
 export type EventComparator = (optimistic: Event, confirmed: Event) => boolean;
 
+/**
+ * EventOrderer is used to determine the order of elements in the event buffer. It expects
+ * to return a negative value of the first argument is less than the second argument, zero
+ * if they are equal, and a positive value otherwise.
+ */
+export type EventOrderer = (a: AblyTypes.Message, b: AblyTypes.Message) => number;
+
 /**
  * MutationOptions can be used to configure options on individual mutations.
  */