From 847264253ec4efd0227428e852b3a2eb12fb07d7 Mon Sep 17 00:00:00 2001
From: Ben Durrant <ben.j.durrant@gmail.com>
Date: Mon, 20 Nov 2023 15:28:59 +0000
Subject: [PATCH 1/3] Add isAction type predicate

---
 src/index.ts               |  2 ++
 src/utils/isAction.ts      | 10 ++++++++++
 src/utils/isPlainObject.ts |  2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 src/utils/isAction.ts

diff --git a/src/index.ts b/src/index.ts
index 8bdd6c4e7c..26881bebfa 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -4,6 +4,7 @@ import combineReducers from './combineReducers'
 import bindActionCreators from './bindActionCreators'
 import applyMiddleware from './applyMiddleware'
 import compose from './compose'
+import isAction from './utils/isAction'
 import __DO_NOT_USE__ActionTypes from './utils/actionTypes'
 
 // types
@@ -42,5 +43,6 @@ export {
   bindActionCreators,
   applyMiddleware,
   compose,
+  isAction,
   __DO_NOT_USE__ActionTypes
 }
diff --git a/src/utils/isAction.ts b/src/utils/isAction.ts
new file mode 100644
index 0000000000..878f4a8096
--- /dev/null
+++ b/src/utils/isAction.ts
@@ -0,0 +1,10 @@
+import { Action } from '../types/actions'
+import isPlainObject from './isPlainObject'
+
+export default function isAction(action: unknown): action is Action<string> {
+  return (
+    isPlainObject(action) &&
+    'type' in action &&
+    typeof (action as Record<'type', unknown>).type === 'string'
+  )
+}
diff --git a/src/utils/isPlainObject.ts b/src/utils/isPlainObject.ts
index 9d1956328a..de6a260af0 100644
--- a/src/utils/isPlainObject.ts
+++ b/src/utils/isPlainObject.ts
@@ -2,7 +2,7 @@
  * @param obj The object to inspect.
  * @returns True if the argument appears to be a plain object.
  */
-export default function isPlainObject(obj: any): boolean {
+export default function isPlainObject(obj: any): obj is object {
   if (typeof obj !== 'object' || obj === null) return false
 
   let proto = obj

From 7859c01b4c922e1b7b171561f91a1d605a7f8d94 Mon Sep 17 00:00:00 2001
From: Ben Durrant <ben.j.durrant@gmail.com>
Date: Mon, 20 Nov 2023 15:33:16 +0000
Subject: [PATCH 2/3] tests

---
 test/utils/isAction.spec.ts | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 test/utils/isAction.spec.ts

diff --git a/test/utils/isAction.spec.ts b/test/utils/isAction.spec.ts
new file mode 100644
index 0000000000..029189f265
--- /dev/null
+++ b/test/utils/isAction.spec.ts
@@ -0,0 +1,23 @@
+import { isAction } from 'redux'
+
+describe('isAction', () => {
+  it('should only return true for plain objects with a string type property', () => {
+    const actionCreator = () => ({ type: 'anAction' })
+    class Action {
+      type = 'totally an action'
+    }
+    const testCases: [action: unknown, expected: boolean][] = [
+      [{ type: 'an action' }, true],
+      [{ type: 'more props', extra: true }, true],
+      [{ type: 0 }, false],
+      [actionCreator(), true],
+      [actionCreator, false],
+      [Promise.resolve({ type: 'an action' }), false],
+      [new Action(), false],
+      ['a string', false]
+    ]
+    for (const [action, expected] of testCases) {
+      expect(isAction(action)).toBe(expected)
+    }
+  })
+})

From d44a074b6ac1f6626d11fdeffea782cb52e6007a Mon Sep 17 00:00:00 2001
From: Ben Durrant <ben.j.durrant@gmail.com>
Date: Mon, 20 Nov 2023 15:33:47 +0000
Subject: [PATCH 3/3] use internal import

---
 test/utils/isAction.spec.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/utils/isAction.spec.ts b/test/utils/isAction.spec.ts
index 029189f265..165495e902 100644
--- a/test/utils/isAction.spec.ts
+++ b/test/utils/isAction.spec.ts
@@ -1,4 +1,4 @@
-import { isAction } from 'redux'
+import isAction from '@internal/utils/isAction'
 
 describe('isAction', () => {
   it('should only return true for plain objects with a string type property', () => {