feat: add isPlainObject type guard (#16)

* feat: add `isPlainObject` type guard

* docs: add isPlainObject

docs/typed/is-plain-object.mdx

@@ -0,0 +1,20 @@
+---
+title: isPlainObject
+description: 'Determine if a value is a plain object'
+group: Typed
+---
+
+## Basic usage
+
+Pass in a value and get a boolean telling you if the value is a plain object.
+
+```ts
+import { isPlainObject } from 'radash'
+
+isPlainObject({}) // => true
+isPlainObject(Object.create(null)) // => true
+
+isPlainObject([]) // => false
+isPlainObject(null) // => false
+isPlainObject(new Date()) // => false
+```

src/index.ts

@@ -96,6 +96,7 @@ export {
   isIntString,
   isNumber,
   isObject,
+  isPlainObject,
   isPrimitive,
   isPromise,
   isString,

src/tests/typed.test.ts

@@ -78,6 +78,33 @@ describe('typed module', () => {
     })
   })
 
+  describe('isPlainObject function', () => {
+    test('returns true for object literal', () => {
+      const result = _.isPlainObject({})
+      expect(result).toBeTruthy()
+    })
+    test('returns true for Object.create(null)', () => {
+      const result = _.isPlainObject(Object.create(null))
+      expect(result).toBeTruthy()
+    })
+    test('returns false for non-plain object', () => {
+      const result = _.isPlainObject(new Date())
+      expect(result).toBeFalsy()
+    })
+    test('returns false for array', () => {
+      const result = _.isPlainObject([1, 2, 3])
+      expect(result).toBeFalsy()
+    })
+    test('returns false for null', () => {
+      const result = _.isPlainObject(null)
+      expect(result).toBeFalsy()
+    })
+    test('returns false for undefined', () => {
+      const result = _.isPlainObject(undefined)
+      expect(result).toBeFalsy()
+    })
+  })
+
   describe('isPrimitive function', () => {
     test('returns true for all the primitives', () => {
       const arr = [

src/typed.ts

@@ -1,3 +1,5 @@
+const toString = /* @__PURE__ */ Object.prototype.toString
+
 export const isSymbol = (value: any): value is symbol => {
   return !!value && value.constructor === Symbol
 }
@@ -8,6 +10,14 @@ export const isObject = (value: any): value is object => {
   return !!value && value.constructor === Object
 }
 
+export const isPlainObject = (value: any): value is object => {
+  if (toString.call(value) !== '[object Object]') {
+    return false
+  }
+  const proto = Object.getPrototypeOf(value)
+  return proto === null || proto === Object.getPrototypeOf({})
+}
+
 /**
  * Checks if the given value is primitive.
  *
@@ -55,7 +65,7 @@ export const isNumber = (value: any): value is number => {
 }
 
 export const isDate = (value: any): value is Date => {
-  return Object.prototype.toString.call(value) === '[object Date]'
+  return toString.call(value) === '[object Date]'
 }
 
 /**