improve guards

src/wrapper.ts

@@ -44,7 +44,7 @@ export namespace Signal {
     #brand() {}
 
     static {
-      isState = (s) => #brand in s;
+      isState = (s) => typeof s === "object" && #brand in s;
     }
 
     constructor(initialValue: T, options: Signal.Options<T> = {}) {
@@ -84,7 +84,7 @@ export namespace Signal {
     #brand() {}
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     static {
-      isComputed = (c: any) => #brand in c;
+      isComputed = (c: any) => typeof c === "object" && #brand in c;
     }
 
     // Create a Signal which evaluates to the value returned by the callback.

tests/behaviors/guards.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { Signal } from "../../src/wrapper.js";
+
+describe("Guards", () => {
+  it("should work with Signals", () => {
+    const state = new Signal.State(1);
+    const computed = new Signal.Computed(() => state.get() * 2);
+    expect(Signal.isState(state)).toBe(true);
+    expect(Signal.isComputed(state)).toBe(false);
+
+    expect(Signal.isState(computed)).toBe(false);
+    expect(Signal.isComputed(computed)).toBe(true);
+  });
+
+  it("shouldn't error with values", () => {
+    expect(Signal.isState(1)).toBe(false);
+    expect(Signal.isComputed(2)).toBe(false);
+
+    expect(Signal.isState({})).toBe(false);
+    expect(Signal.isComputed({})).toBe(false);
+  });
+});