fix throttle function not being able to run with argument(s)

src/presentation/components/Shared/Throttle.ts

@@ -1,20 +1,10 @@
-export function throttle<T extends []>(
-    callback: (..._: T) => void, wait: number,
-    timer: ITimer = NodeTimer): (..._: T) => void {
-    let queuedToRun: ReturnType<typeof setTimeout>;
-    let previouslyRun: number;
-    return function invokeFn(...args: T) {
-        const now = timer.dateNow();
-        if (queuedToRun) {
-            queuedToRun = timer.clearTimeout(queuedToRun) as undefined;
-        }
-        if (!previouslyRun || (now - previouslyRun >= wait)) {
-            callback(...args);
-            previouslyRun = now;
-        } else {
-            queuedToRun = timer.setTimeout(invokeFn.bind(null, ...args), wait - (now - previouslyRun));
-        }
-    };
+export type CallbackType = (..._: any[]) => void;
+
+export function throttle(
+    callback: CallbackType, waitInMs: number,
+    timer: ITimer = NodeTimer): CallbackType {
+    const throttler = new Throttler(timer, waitInMs, callback);
+    return (...args: any[]) => throttler.invoke(...args);
 }
 
 export interface ITimer {
@@ -28,3 +18,35 @@ const NodeTimer: ITimer = {
     clearTimeout: (timeoutId) => clearTimeout(timeoutId),
     dateNow: () => Date.now(),
 };
+
+interface IThrottler {
+    invoke: CallbackType;
+}
+
+class Throttler implements IThrottler {
+    private queuedToRun: ReturnType<typeof setTimeout>;
+    private previouslyRun: number;
+    constructor(
+        private readonly timer: ITimer,
+        private readonly waitInMs: number,
+        private readonly callback: CallbackType) {
+        if (!timer) { throw new Error('undefined timer'); }
+        if (!waitInMs) { throw new Error('no delay to throttle'); }
+        if (waitInMs < 0) { throw new Error('negative delay'); }
+        if (!callback) { throw new Error('undefined callback'); }
+    }
+    public invoke(...args: any[]): void {
+        const now = this.timer.dateNow();
+        if (this.queuedToRun) {
+            this.queuedToRun = this.timer.clearTimeout(this.queuedToRun) as undefined;
+        }
+        if (!this.previouslyRun || (now - this.previouslyRun >= this.waitInMs)) {
+            this.callback(...args);
+            this.previouslyRun = now;
+        } else {
+            const nextCall = () => this.invoke(...args);
+            const nextCallDelayInMs = this.waitInMs - (now - this.previouslyRun);
+            this.queuedToRun = this.timer.setTimeout(nextCall, nextCallDelayInMs);
+        }
+    }
+}

tests/unit/presentation/components/Shared/Throttle.spec.ts

@@ -5,6 +5,32 @@ import { EventSource } from '@/infrastructure/Events/EventSource';
 import { IEventSubscription } from '@/infrastructure/Events/IEventSource';
 
 describe('throttle', () => {
+    it('throws if callback is undefined', () => {
+        // arrange
+        const expectedError = 'undefined callback';
+        const callback = undefined;
+        // act
+        const act = () => throttle(callback, 500);
+        // assert
+        expect(act).to.throw(expectedError);
+    });
+    describe('throws if waitInMs is negative or zero', () => {
+        // arrange
+        const testCases = [
+            { value: 0, expectedError: 'no delay to throttle' },
+            { value: -2, expectedError: 'negative delay' },
+        ];
+        const callback = () => { return; };
+        for (const testCase of testCases) {
+            it(`"${testCase.value}" throws "${testCase.expectedError}"`, () => {
+                // act
+                const waitInMs = testCase.value;
+                const act = () => throttle(callback, waitInMs);
+                // assert
+                expect(act).to.throw(testCase.expectedError);
+            });
+        }
+    });
     it('should call the callback immediately', () => {
         // arrange
         const timer = new TimerMock();
@@ -21,16 +47,17 @@ describe('throttle', () => {
         const timer = new TimerMock();
         let totalRuns = 0;
         const callback = () => totalRuns++;
-        const throttleFunc = throttle(callback, 500, timer);
+        const waitInMs = 500;
+        const throttleFunc = throttle(callback, waitInMs, timer);
         // act
         throttleFunc();
-        totalRuns--;
+        totalRuns--; // So we don't count the initial run
         throttleFunc();
-        timer.tick(500);
+        timer.tickNext(waitInMs);
         // assert
         expect(totalRuns).to.equal(1);
     });
-    it('calls the callback at most once at given time', () => {
+    it('should call the callback at most once at given time', () => {
         // arrange
         const timer = new TimerMock();
         let totalRuns = 0;
@@ -40,11 +67,43 @@ describe('throttle', () => {
         const throttleFunc = throttle(callback, waitInMs, timer);
         // act
         for (let i = 0; i < totalCalls; i++) {
-            timer.tick(waitInMs / totalCalls * i);
+            timer.setCurrentTime(waitInMs / totalCalls * i);
+            throttleFunc();
+        }
+        // assert
+        expect(totalRuns).to.equal(2); // one initial and one at the end
+    });
+    it('should call the callback as long as delay is waited', () => {
+        // arrange
+        const timer = new TimerMock();
+        let totalRuns = 0;
+        const callback = () => totalRuns++;
+        const waitInMs = 500;
+        const expectedTotalRuns = 10;
+        const throttleFunc = throttle(callback, waitInMs, timer);
+        // act
+        for (let i = 0; i < expectedTotalRuns; i++) {
             throttleFunc();
+            timer.tickNext(waitInMs);
         }
         // assert
-        expect(totalRuns).to.equal(2); // initial and at the end
+        expect(totalRuns).to.equal(expectedTotalRuns);
+    });
+    it('should call arguments as expected', () => {
+        // arrange
+        const timer = new TimerMock();
+        const expected = [ 1, 2, 3 ];
+        const actual = new Array<number>();
+        const callback = (arg: number) => { actual.push(arg); };
+        const waitInMs = 500;
+        const throttleFunc = throttle(callback, waitInMs, timer);
+        // act
+        for (const arg of expected) {
+            throttleFunc(arg);
+            timer.tickNext(waitInMs);
+        }
+        // assert
+        expect(expected).to.deep.equal(actual);
     });
 });
 
@@ -69,7 +128,10 @@ class TimerMock implements ITimer {
     public dateNow(): number {
         return this.currentTime;
     }
-    public tick(ms: number): void {
+    public tickNext(ms: number): void {
+        this.setCurrentTime(this.currentTime + ms);
+    }
+    public setCurrentTime(ms: number): void {
         this.currentTime = ms;
         this.timeChanged.notify(this.currentTime);
     }