feat: throttle function (#483)

packages/utilities/package.json

@@ -261,6 +261,11 @@
 			"import": "./dist/lib/splitText.mjs",
 			"require": "./dist/lib/splitText.js"
 		},
+		"./throttle": {
+			"types": "./dist/lib/throttle.d.ts",
+			"import": "./dist/lib/throttle.mjs",
+			"require": "./dist/lib/throttle.js"
+		},
 		"./toTitleCase": {
 			"types": "./dist/lib/toTitleCase.d.ts",
 			"import": "./dist/lib/toTitleCase.mjs",

packages/utilities/src/index.ts

@@ -37,6 +37,7 @@ export * from './lib/regExpEsc';
 export * from './lib/roundNumber';
 export { AbortError, sleep, sleepSync, type SleepOptions } from './lib/sleep';
 export * from './lib/splitText';
+export { throttle, type ThrottleFn } from './lib/throttle';
 export { toTitleCase, type ToTitleCaseOptions } from './lib/toTitleCase';
 export * from './lib/tryParseJSON';
 export * from './lib/tryParseURL';

packages/utilities/src/lib/throttle.ts

@@ -0,0 +1,33 @@
+export type ThrottleFn<T extends (...args: any[]) => any> = T & { flush: () => void };
+
+/**
+ * Creates a throttled function that only invokes `func` at most once per
+ * every `wait` milliseconds. The throttled function comes with a `flush` method to
+ * reset the last time the throttled function was invoked.
+ *
+ * @param func The function to throttle.
+ * @param wait The number of milliseconds to throttle invocations to.
+ *
+ * @returns Returns the new throttled function.
+ */
+export function throttle<T extends (...args: any[]) => any>(func: T, wait: number): ThrottleFn<T> {
+	let prev = 0;
+	let prevValue: ReturnType<T>;
+
+	return Object.assign(
+		(...args: Parameters<T>) => {
+			const now = Date.now();
+			if (now - prev > wait) {
+				prev = now;
+				return (prevValue = func(...args));
+			}
+
+			return prevValue;
+		},
+		{
+			flush() {
+				prev = 0;
+			}
+		}
+	) as ThrottleFn<T>;
+}

packages/utilities/tests/throttle.test.ts

@@ -0,0 +1,26 @@
+import { throttle, sleep } from '../src';
+
+describe('throttle', () => {
+	test('GIVEN number callback THEN returns the same output until the delay', async () => {
+		const callback = vi.fn((num: number) => num);
+
+		const throttleFunc = throttle(callback, 50);
+		const now = Date.now();
+		expect(throttleFunc(now)).toEqual(now);
+		expect(throttleFunc(100)).toEqual(now);
+		expect(callback).toHaveBeenCalledOnce();
+		await sleep(100);
+		expect(throttleFunc(250)).toEqual(250);
+	});
+
+	test('GIVEN number callback THEN returns the new output when flush', () => {
+		const callback = vi.fn((num: number) => num);
+
+		const throttleFunc = throttle(callback, 100);
+		const now = Date.now();
+		expect(throttleFunc(now)).toEqual(now);
+		throttleFunc.flush();
+		expect(throttleFunc(100)).toEqual(100);
+		expect(callback).toHaveBeenCalledTimes(2);
+	});
+});