Bump to v4.0.0.

isPlainObject.js

@@ -0,0 +1,68 @@
+import isHostObject from './internal/isHostObject';
+import isObjectLike from './isObjectLike';
+
+/** `Object#toString` result references. */
+var objectTag = '[object Object]';
+
+/** Used for built-in method references. */
+var objectProto = Object.prototype;
+
+/** Used to resolve the decompiled source of functions. */
+var funcToString = Function.prototype.toString;
+
+/** Used to infer the `Object` constructor. */
+var objectCtorString = funcToString.call(Object);
+
+/**
+ * Used to resolve the [`toStringTag`](http://ecma-international.org/ecma-262/6.0/#sec-object.prototype.tostring)
+ * of values.
+ */
+var objectToString = objectProto.toString;
+
+/** Built-in value references. */
+var getPrototypeOf = Object.getPrototypeOf;
+
+/**
+ * Checks if `value` is a plain object, that is, an object created by the
+ * `Object` constructor or one with a `[[Prototype]]` of `null`.
+ *
+ * @static
+ * @memberOf _
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is a plain object, else `false`.
+ * @example
+ *
+ * function Foo() {
+ *   this.a = 1;
+ * }
+ *
+ * _.isPlainObject(new Foo);
+ * // => false
+ *
+ * _.isPlainObject([1, 2, 3]);
+ * // => false
+ *
+ * _.isPlainObject({ 'x': 0, 'y': 0 });
+ * // => true
+ *
+ * _.isPlainObject(Object.create(null));
+ * // => true
+ */
+function isPlainObject(value) {
+  if (!isObjectLike(value) || objectToString.call(value) != objectTag || isHostObject(value)) {
+    return false;
+  }
+  var proto = objectProto;
+  if (typeof value.constructor == 'function') {
+    proto = getPrototypeOf(value);
+  }
+  if (proto === null) {
+    return true;
+  }
+  var Ctor = proto.constructor;
+  return (typeof Ctor == 'function' &&
+    Ctor instanceof Ctor && funcToString.call(Ctor) == objectCtorString);
+}
+
+export default isPlainObject;