add entry for isPlainObject

README.md

@@ -163,6 +163,7 @@ For more information, see [Configuring the ESLint Plugin](configuring.md)
 1. [_.has](#_has)
 1. [_.get](#_get)
 1. [_.invert](#_invert)
+1. [_.isPlainObject](#_isplainobject)
 1. [_.keys](#_keys)
 1. [_.mapKeys](#_mapKeys)
 1. [_.omit](#_omit)
@@ -2264,6 +2265,46 @@ Checks if value is an integer.
 
 **[⬆ back to top](#quick-links)**
 
+### _.isPlainObject
+
+Checks if value is a plain object, that is, an object created by the Object constructor or one with a [[Prototype]] of null.
+
+  ```js
+  var object = { 'a': 1, 'b': 2, 'c': 1 };
+
+  // Underscore/Lodash
+  var result = _.isPlainObject(object);
+  console.log(result)
+  // output: true
+
+  function isPlainObject(value) {
+    if (typeof value !== 'object' || value === null) return false
+
+    if (Object.prototype.toString.call(value) !== '[object Object]') return false
+
+    const proto = Object.getPrototypeOf(value);
+    if (proto === null) return true
+
+    const Ctor = Object.prototype.hasOwnProperty.call(proto, 'constructor') && proto.constructor;
+    return (
+        typeof Ctor === 'function' &&
+        Ctor instanceof Ctor && Function.prototype.call(Ctor) === Function.prototype.call(value)
+    );
+
+    var result = invert(object);
+    console.log(result)
+    // output: true
+    }
+  ```
+
+#### Browser Support for `Object.getPrototypeOf()`
+
+![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
+:-: | :-: | :-: | :-: | :-: | :-: |
+  5.0 ✔  | 12.0 ✔  | 3.5 ✔ |  ✖  |  12.1 ✔ |  5.0 ✔ |
+
+**[⬆ back to top](#quick-links)**
+
 ### _.isNaN
 
 Checks if a value is NaN.

tests/unit/all.js

@@ -299,6 +299,69 @@ describe('code snippet example', () => {
        )
     })
   })
+  describe('isPlainObject', () => {
+    function isPlainObject(value) {
+      if (typeof value !== 'object' || value === null) return false
+
+      if (Object.prototype.toString.call(value) !== '[object Object]') return false
+
+      const proto = Object.getPrototypeOf(value);
+      if (proto === null) return true
+
+      const Ctor = Object.prototype.hasOwnProperty.call(proto, 'constructor') && proto.constructor;
+      return (
+          typeof Ctor === 'function' &&
+          Ctor instanceof Ctor && Function.prototype.call(Ctor) === Function.prototype.call(value)
+      );
+    }
+
+    function Foo() {
+      this.a = 1;
+    }
+
+    it('_.isPlainObject(NaN)', () => {
+      assert.equal(
+      _.isPlainObject(NaN),
+      isPlainObject(NaN)
+      )
+    })
+    it('_.isPlainObject([1, 2, 3])', () => {
+      assert.equal(
+      _.isPlainObject([1, 2, 3]),
+      isPlainObject([1, 2, 3])
+      )
+    })
+    it('_.isPlainObject(null)', () => {
+      assert.equal(
+      _.isPlainObject(null),
+      isPlainObject(null)
+      )
+    })
+    it("_.isPlainObject({ 'x': 0, 'y': 0 })", () => {
+      assert.equal(
+      _.isPlainObject({ 'x': 0, 'y': 0 }),
+      isPlainObject({ 'x': 0, 'y': 0 })
+      )
+    })
+    it("_.isPlainObject(Object.create(null))", () => {
+      assert.equal(
+      _.isPlainObject(Object.create(null)),
+      isPlainObject(Object.create(null))
+      )
+    })
+    it("_.isPlainObject(Object.create(new Foo()))", () => {
+      assert.equal(
+      _.isPlainObject(Object.create(new Foo())),
+      isPlainObject(Object.create(new Foo()))
+      )
+    })
+    it("_.isPlainObject(Object.create(new Date()))", () => {
+      assert.equal(
+      _.isPlainObject(Object.create(new Date())),
+      isPlainObject(Object.create(new Date()))
+      )
+    })
+  })
   describe('get', () => {
     const get = (obj, path, defaultValue) => {
       const travel = regexp =>