From 70697d962604130fb0f0b012e1d55bb45017130c Mon Sep 17 00:00:00 2001
From: streamich <streamich@gmail.com>
Date: Thu, 30 May 2019 19:57:10 +0200
Subject: [PATCH 1/3] =?UTF-8?q?style:=20=F0=9F=92=84=20fix=20linting=20err?=
 =?UTF-8?q?or?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/useSetState.ts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/useSetState.ts b/src/useSetState.ts
index 056eaca6..d0900439 100644
--- a/src/useSetState.ts
+++ b/src/useSetState.ts
@@ -1,6 +1,8 @@
 import { useState } from 'react';
 
-const useSetState = <T extends object>(initialState: T = {} as T): [T, (patch: Partial<T> | ((prevState: T) => Partial<T>)) => void] => {
+const useSetState = <T extends object>(
+  initialState: T = {} as T
+): [T, (patch: Partial<T> | ((prevState: T) => Partial<T>)) => void] => {
   const [state, set] = useState<T>(initialState);
   const setState = patch => {
     set(prevState => Object.assign({}, prevState, patch instanceof Function ? patch(prevState) : patch));

From d0c3713decc27c5587ad1d60809288d019ea608d Mon Sep 17 00:00:00 2001
From: streamich <streamich@gmail.com>
Date: Thu, 30 May 2019 20:39:07 +0200
Subject: [PATCH 2/3] =?UTF-8?q?feat:=20=F0=9F=8E=B8=20improve=20useObserva?=
 =?UTF-8?q?ble()=20type=20annotations?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/useObservable.ts | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/useObservable.ts b/src/useObservable.ts
index 14a48286..49832492 100644
--- a/src/useObservable.ts
+++ b/src/useObservable.ts
@@ -1,6 +1,16 @@
 import { useEffect, useState } from 'react';
 
-const useObservable = <T>(observable$, initialValue?: T): T | undefined => {
+export interface Observable<T> {
+  subscribe: (
+    listener: (value: T) => void
+  ) => {
+    unsubscribe: () => void;
+  };
+}
+
+function useObservable<T>(observable$: Observable<T>): T | undefined;
+function useObservable<T>(observable$: Observable<T>, initialValue: T): T;
+function useObservable<T>(observable$: Observable<T>, initialValue?: T): T | undefined {
   const [value, update] = useState<T | undefined>(initialValue);
 
   useEffect(() => {
@@ -9,6 +19,6 @@ const useObservable = <T>(observable$, initialValue?: T): T | undefined => {
   }, [observable$]);
 
   return value;
-};
+}
 
 export default useObservable;

From 3a0c683099bb224fddd2d7226e81a51589a6e621 Mon Sep 17 00:00:00 2001
From: streamich <streamich@gmail.com>
Date: Thu, 30 May 2019 20:43:53 +0200
Subject: [PATCH 3/3] =?UTF-8?q?test:=20=F0=9F=92=8D=20add=20tests=20for=20?=
 =?UTF-8?q?useObservable()=20hook?=
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

---
 babel.config.js                      |  1 +
 package.json                         |  1 +
 src/__tests__/useObservable.test.tsx | 35 ++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 src/__tests__/useObservable.test.tsx

diff --git a/babel.config.js b/babel.config.js
index 4bea0c59..b8339150 100644
--- a/babel.config.js
+++ b/babel.config.js
@@ -1,3 +1,4 @@
 module.exports = {
     presets: ['@babel/preset-env', '@babel/preset-react', "@babel/preset-typescript"],
+    plugins: ['@babel/plugin-syntax-dynamic-import']
 };
\ No newline at end of file
diff --git a/package.json b/package.json
index 0a4294b8..c476782b 100644
--- a/package.json
+++ b/package.json
@@ -44,6 +44,7 @@
   },
   "homepage": "https://github.com/streamich/react-use#readme",
   "dependencies": {
+    "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "copy-to-clipboard": "^3.1.0",
     "nano-css": "^5.1.0",
     "react-fast-compare": "^2.0.4",
diff --git a/src/__tests__/useObservable.test.tsx b/src/__tests__/useObservable.test.tsx
new file mode 100644
index 00000000..6bba8c87
--- /dev/null
+++ b/src/__tests__/useObservable.test.tsx
@@ -0,0 +1,35 @@
+import { act, renderHook } from 'react-hooks-testing-library';
+import { Subject } from 'rxjs';
+import { useObservable } from '..';
+
+test('default initial value is undefined', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$));
+
+  expect(result.current).toBe(undefined);
+});
+
+test('can specify initial value', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$, 123));
+
+  expect(result.current).toBe(123);
+});
+
+test('returns the latest value of observables', () => {
+  const subject$ = new Subject();
+  const { result } = renderHook(() => useObservable(subject$, 123));
+
+  act(() => {
+    subject$.next(125);
+  });
+  expect(result.current).toBe(125);
+
+  act(() => {
+    subject$.next(300);
+    subject$.next(400);
+  });
+  expect(result.current).toBe(400);
+});
+
+xtest('subscribes to observable only once', () => {});