fix(types)!: [ObjectPlain] match pojos only

- https://masteringjs.io/tutorials/fundamentals/pojo

Signed-off-by: Lexus Drumgold <[email protected]>

src/types/__tests__/object-plain.spec-d.ts

@@ -3,15 +3,44 @@
  * @module tutils/types/tests/unit-d/ObjectPlain
  */
 
-import type IndexSignature from '../index-signature'
+import type Class from '../class'
+import type Fn from '../fn'
 import type TestSubject from '../object-plain'
+import type Primitive from '../primitive'
 
 describe('unit-d:types/ObjectPlain', () => {
-  it('should have keys of type IndexSignature', () => {
-    expectTypeOf<keyof TestSubject>().toEqualTypeOf<IndexSignature>()
+  it('should match [[x: string]: unknown]', () => {
+    expectTypeOf<TestSubject[string]>().toBeUnknown()
   })
 
-  it('should have properties of type any', () => {
-    expectTypeOf<TestSubject[IndexSignature]>().toBeAny()
+  it('should match [[x: symbol]: unknown]', () => {
+    expectTypeOf<TestSubject[symbol]>().toBeUnknown()
+  })
+
+  it('should match pojos', () => {
+    expectTypeOf({ 5: null }).toMatchTypeOf<TestSubject>()
+    expectTypeOf({ email: faker.internet.email() }).toMatchTypeOf<TestSubject>()
+  })
+
+  it('should not match arrays', () => {
+    expectTypeOf<string[]>().not.toMatchTypeOf<TestSubject>()
+  })
+
+  it('should not match class objects', () => {
+    expectTypeOf<Class<any>>().not.toMatchTypeOf<TestSubject>()
+  })
+
+  it('should not match class instance objects', () => {
+    expectTypeOf(new Date()).not.toMatchTypeOf<TestSubject>()
+    expectTypeOf(new Map()).not.toMatchTypeOf<TestSubject>()
+    expectTypeOf(new Set()).not.toMatchTypeOf<TestSubject>()
+  })
+
+  it('should not match functions', () => {
+    expectTypeOf<Fn>().not.toMatchTypeOf<TestSubject>()
+  })
+
+  it('should not match primitives', () => {
+    expectTypeOf<Primitive>().not.toMatchTypeOf<TestSubject>()
   })
 })

src/types/object-plain.ts

@@ -3,11 +3,11 @@
  * @module tutils/types/ObjectPlain
  */
 
-import type IndexSignature from './index-signature'
-
 /**
- * A plain object.
+ * Type representing a plain old JavaScript object (POJO).
+ *
+ * @see https://masteringjs.io/tutorials/fundamentals/pojo
  */
-type ObjectPlain = { [Key in IndexSignature]?: any }
+type ObjectPlain = { [K in string | symbol]?: unknown }
 
 export type { ObjectPlain as default }

src/utils/is-object-plain.ts

@@ -7,12 +7,15 @@ import type { ObjectPlain } from '#src/types'
 import isNull from './is-null'
 
 /**
- * Checks if the given `value` is a plain object.
+ * Checks if the given `value` is a plain object (i.e. [POJO][1]).
  *
- * A plain object is an object created by the [`Object`][1] constructor or an
+ * A plain object is an object created by the [`Object`][2] constructor or an
  * object with a `[[Prototype]]` of `null`.
  *
- * [1]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
+ * [1]: https://masteringjs.io/tutorials/fundamentals/pojo
+ * [2]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
+ *
+ * @see {@linkcode ObjectPlain}
  *
  * @param {unknown} value - Value to evaluate
  * @return {value is ObjectPlain} `true` if `value` is plain object