Fix debounce with immediate firing twice on single call (#30082)

test/common/util/debounce.test.ts

@@ -0,0 +1,153 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { debounce } from "../../../src/common/util/debounce";
+
+describe("debounce", () => {
+  beforeEach(() => {
+    vi.useFakeTimers({
+      toFake: ["setTimeout", "clearTimeout"],
+      shouldAdvanceTime: false,
+    });
+    vi.stubGlobal("window", {
+      ...window,
+      setTimeout: globalThis.setTimeout,
+      clearTimeout: globalThis.clearTimeout,
+    });
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    vi.unstubAllGlobals();
+  });
+
+  describe("without immediate", () => {
+    it("calls function after wait period", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500);
+
+      debounced();
+      expect(fn).not.toHaveBeenCalled();
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+
+    it("resets timer on subsequent calls", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500);
+
+      debounced();
+      vi.advanceTimersByTime(300);
+      debounced();
+      vi.advanceTimersByTime(300);
+      expect(fn).not.toHaveBeenCalled();
+
+      vi.advanceTimersByTime(200);
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+
+    it("uses the latest arguments", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500);
+
+      debounced("a");
+      debounced("b");
+      debounced("c");
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(1);
+      expect(fn).toHaveBeenCalledWith("c");
+    });
+  });
+
+  describe("with immediate", () => {
+    it("calls function immediately on first call", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced();
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+
+    it("does not call again on trailing edge for a single call", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced();
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+
+    it("calls trailing edge when there are additional calls during wait", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced("a");
+      expect(fn).toHaveBeenCalledTimes(1);
+      expect(fn).toHaveBeenCalledWith("a");
+
+      debounced("b");
+      debounced("c");
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(2);
+      expect(fn).toHaveBeenLastCalledWith("c");
+    });
+
+    it("does not fire leading edge during cooldown", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced();
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      vi.advanceTimersByTime(200);
+      debounced();
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+
+    it("allows a new leading call after cooldown expires", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced("first");
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      debounced("second");
+      expect(fn).toHaveBeenCalledTimes(2);
+      expect(fn).toHaveBeenLastCalledWith("second");
+    });
+  });
+
+  describe("cancel", () => {
+    it("cancels pending trailing call", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500);
+
+      debounced();
+      debounced.cancel();
+
+      vi.advanceTimersByTime(500);
+      expect(fn).not.toHaveBeenCalled();
+    });
+
+    it("cancels pending trailing call with immediate", () => {
+      const fn = vi.fn();
+      const debounced = debounce(fn, 500, true);
+
+      debounced("a");
+      debounced("b");
+      expect(fn).toHaveBeenCalledTimes(1);
+
+      debounced.cancel();
+
+      vi.advanceTimersByTime(500);
+      expect(fn).toHaveBeenCalledTimes(1);
+    });
+  });
+});