feat(store): add reactive state primitives (#311)

packages/utils/src/predicate/predicate.ts

@@ -37,12 +37,18 @@ export function isObject(value: unknown): value is object {
   return value !== null && typeof value === 'object';
 }
 
+/**
+ * Check if a value is a plain object (not a class instance like Date, Map, etc).
+ */
+export function isPlainObject(value: unknown): value is Record<string, unknown> {
+  if (!isObject(value)) return false;
+  const proto = Object.getPrototypeOf(value);
+  return proto === null || proto === Object.prototype;
+}
+
 /**
  * Check if a value is an AbortError.
  */
 export function isAbortError(value: unknown): value is Error {
-  return (
-    value instanceof Error
-    && value.name === 'AbortError'
-  );
+  return value instanceof Error && value.name === 'AbortError';
 }

packages/utils/src/predicate/tests/predicate.test.ts

@@ -8,6 +8,7 @@ import {
   isNull,
   isNumber,
   isObject,
+  isPlainObject,
   isPromise,
   isString,
   isUndefined,
@@ -175,6 +176,44 @@ describe('predicate', () => {
     });
   });
 
+  describe('isPlainObject', () => {
+    it('returns true for plain objects', () => {
+      expect(isPlainObject({})).toBe(true);
+      expect(isPlainObject({ a: 1 })).toBe(true);
+      expect(isPlainObject(Object.create(null))).toBe(true);
+      expect(isPlainObject(new Object())).toBe(true);
+    });
+
+    it('returns false for arrays', () => {
+      expect(isPlainObject([])).toBe(false);
+      expect(isPlainObject([1, 2, 3])).toBe(false);
+    });
+
+    it('returns false for class instances', () => {
+      class Foo {}
+      expect(isPlainObject(new Foo())).toBe(false);
+      expect(isPlainObject(new Date())).toBe(false);
+      expect(isPlainObject(new Map())).toBe(false);
+      expect(isPlainObject(new Set())).toBe(false);
+      expect(isPlainObject(/regex/)).toBe(false);
+    });
+
+    it('returns false for primitives', () => {
+      expect(isPlainObject(null)).toBe(false);
+      expect(isPlainObject(undefined)).toBe(false);
+      expect(isPlainObject('string')).toBe(false);
+      expect(isPlainObject(123)).toBe(false);
+      expect(isPlainObject(true)).toBe(false);
+      // eslint-disable-next-line symbol-description
+      expect(isPlainObject(Symbol())).toBe(false);
+    });
+
+    it('returns false for functions', () => {
+      expect(isPlainObject(() => {})).toBe(false);
+      expect(isPlainObject(() => {})).toBe(false);
+    });
+  });
+
   describe('isAbortError', () => {
     it('returns true for AbortError', () => {
       const error = new DOMException('Aborted', 'AbortError');