From 68338db2bc909671a6d0ed943aa0480f725b5714 Mon Sep 17 00:00:00 2001
From: Thammi <thammi@chaossource.net>
Date: Wed, 26 Feb 2020 16:19:57 +0100
Subject: [PATCH 1/3] Accept falsy initalValue

---
 src/index.js       | 25 +++++++++++++++----------
 test/index.test.js |  7 +++++++
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/index.js b/src/index.js
index a2021e7..df7176e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,5 @@
 export default (...args) => {
-  const initialState = typeof args[0] !== 'function' && args.shift();
+  const initialState = typeof args[0] !== 'function' ? args.shift() : null;
   const reducers = args;
 
   if (typeof initialState === 'undefined') {
@@ -12,18 +12,23 @@ export default (...args) => {
     const prevStateIsUndefined = typeof prevState === 'undefined';
     const valueIsUndefined = typeof value === 'undefined';
 
-    if (prevStateIsUndefined && valueIsUndefined && initialState) {
+    if (prevStateIsUndefined && valueIsUndefined && initialState != null) {
       return initialState;
     }
 
-    return reducers.reduce((newState, reducer, index) => {
-      if (typeof reducer === 'undefined') {
-        throw new TypeError(
-          `An undefined reducer was passed in at index ${index}`
-        );
-      }
+    return reducers.reduce(
+      (newState, reducer, index) => {
+        if (typeof reducer === 'undefined') {
+          throw new TypeError(
+            `An undefined reducer was passed in at index ${index}`
+          );
+        }
 
-      return reducer(newState, value, ...args);
-    }, prevStateIsUndefined && !valueIsUndefined && initialState ? initialState : prevState);
+        return reducer(newState, value, ...args);
+      },
+      prevStateIsUndefined && !valueIsUndefined && initialState != null
+        ? initialState
+        : prevState
+    );
   };
 };
diff --git a/test/index.test.js b/test/index.test.js
index 0da5619..c1d6f92 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -20,6 +20,13 @@ test('passes `initialState` when state is `undefined` and value is defined', ()
   expect(reducer(undefined, 1)).toEqual({ A: 1, B: 0 });
 });
 
+test('passes falsy `initialState` when state is `undefined` and value is defined', () => {
+  const initialState = '';
+  const reducer = reduceReducers(initialState, (state, payload) => state);
+
+  expect(reducer(undefined, 1)).toEqual('');
+});
+
 test('throws an error if initialState is undefined', () => {
   expect(() => {
     reduceReducers(undefined);

From 8bf8e2c4df102856e2566a866fd220c0a5dde35e Mon Sep 17 00:00:00 2001
From: Thammi <thammi@chaossource.net>
Date: Wed, 26 Feb 2020 16:39:01 +0100
Subject: [PATCH 2/3] Minor stylistic change for check against initialValue

---
 src/index.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/index.js b/src/index.js
index df7176e..f2362d6 100644
--- a/src/index.js
+++ b/src/index.js
@@ -12,7 +12,7 @@ export default (...args) => {
     const prevStateIsUndefined = typeof prevState === 'undefined';
     const valueIsUndefined = typeof value === 'undefined';
 
-    if (prevStateIsUndefined && valueIsUndefined && initialState != null) {
+    if (prevStateIsUndefined && valueIsUndefined && initialState !== null) {
       return initialState;
     }
 
@@ -26,7 +26,7 @@ export default (...args) => {
 
         return reducer(newState, value, ...args);
       },
-      prevStateIsUndefined && !valueIsUndefined && initialState != null
+      prevStateIsUndefined && !valueIsUndefined && initialState !== null
         ? initialState
         : prevState
     );

From 10adc2558c8bf983432ffb705c056bff3f0704f4 Mon Sep 17 00:00:00 2001
From: Thammi <thammi@chaossource.net>
Date: Wed, 26 Feb 2020 16:48:06 +0100
Subject: [PATCH 3/3] Make linter happy

---
 src/index.js       | 2 +-
 test/index.test.js | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/index.js b/src/index.js
index f2362d6..d3e994f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,5 @@
 export default (...args) => {
-  const initialState = typeof args[0] !== 'function' ? args.shift() : null;
+  const initialState = typeof args[0] === 'function' ? null : args.shift();
   const reducers = args;
 
   if (typeof initialState === 'undefined') {
diff --git a/test/index.test.js b/test/index.test.js
index c1d6f92..bd00811 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -22,7 +22,7 @@ test('passes `initialState` when state is `undefined` and value is defined', ()
 
 test('passes falsy `initialState` when state is `undefined` and value is defined', () => {
   const initialState = '';
-  const reducer = reduceReducers(initialState, (state, payload) => state);
+  const reducer = reduceReducers(initialState, state => state);
 
   expect(reducer(undefined, 1)).toEqual('');
 });