HUGE sidebar and typing performance improvements (#516)

packages/common-lib/debounce.test.ts

@@ -0,0 +1,76 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { debounce } from "./debounce";
+
+describe("debounce", () => {
+  beforeEach(() => vi.useFakeTimers());
+  afterEach(() => vi.useRealTimers());
+
+  it("calls once with the latest args after the delay", () => {
+    const fn = vi.fn();
+    const d = debounce(fn, 100);
+
+    d("a");
+    d("b");
+    d("c");
+    expect(fn).not.toHaveBeenCalled();
+
+    vi.advanceTimersByTime(100);
+    expect(fn).toHaveBeenCalledExactlyOnceWith("c");
+  });
+
+  it("flush invokes a pending call immediately", () => {
+    const fn = vi.fn();
+    const d = debounce(fn, 100);
+
+    d("a");
+    d("b");
+    d.flush();
+    expect(fn).toHaveBeenCalledExactlyOnceWith("b");
+
+    // The scheduled call was cancelled, so waiting out the delay adds nothing
+    vi.advanceTimersByTime(100);
+    expect(fn).toHaveBeenCalledOnce();
+  });
+
+  it("flush is a no-op with nothing pending", () => {
+    const fn = vi.fn();
+    const d = debounce(fn, 100);
+
+    d.flush();
+    expect(fn).not.toHaveBeenCalled();
+
+    d("a");
+    vi.advanceTimersByTime(100);
+    d.flush();
+    expect(fn).toHaveBeenCalledExactlyOnceWith("a");
+  });
+
+  it("cancel drops the pending call and its args", () => {
+    const fn = vi.fn();
+    const d = debounce(fn, 100);
+
+    d("a");
+    d.cancel();
+    vi.advanceTimersByTime(100);
+    expect(fn).not.toHaveBeenCalled();
+
+    // A cancelled call must not leak its args into the next one
+    d.flush();
+    expect(fn).not.toHaveBeenCalled();
+  });
+
+  it("starts a fresh delay after firing", () => {
+    const fn = vi.fn();
+    const d = debounce(fn, 100);
+
+    d("a");
+    vi.advanceTimersByTime(100);
+    d("b");
+    vi.advanceTimersByTime(99);
+    expect(fn).toHaveBeenCalledOnce();
+
+    vi.advanceTimersByTime(1);
+    expect(fn).toHaveBeenCalledTimes(2);
+    expect(fn).toHaveBeenLastCalledWith("b");
+  });
+});