From 966af4aaee360b743d95b7e174aec4aae3bd4d5b Mon Sep 17 00:00:00 2001
From: ZHAO Jinxiang <xiaoxiangmoe@gmail.com>
Date: Mon, 17 Dec 2018 21:12:38 +0800
Subject: [PATCH] feat: use discriminated union in useAsync

---
 docs/useAsync.md | 10 ++++++----
 package.json     |  2 +-
 src/useAsync.ts  | 16 ++++++++++++----
 3 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/docs/useAsync.md b/docs/useAsync.md
index 4757cc9350..bb5d071e40 100644
--- a/docs/useAsync.md
+++ b/docs/useAsync.md
@@ -17,13 +17,15 @@ const fn = () => new Promise((resolve) => {
 });
 
 const Demo = () => {
-  const {loading, value, error} = useAsync(fn);
+  const state = useAsync(fn);
 
   return (
     <div>
-      {loading
-        ? <div>Loading...</div>
-        : <div>Value: {value}</div>
+      {state.loading?
+        <div>Loading...</div>
+        : state.error?
+        <div>Error...</div>
+        : <div>Value: {state.value}</div>
       }
     </div>
   );
diff --git a/package.json b/package.json
index 477294be71..3d24e6c3e3 100644
--- a/package.json
+++ b/package.json
@@ -43,7 +43,7 @@
     "@storybook/react": "^3.4.11",
     "react": "next",
     "react-dom": "next",
-    "typescript": "^3.1.3",
+    "typescript": "^3.2.2",
     "ts-node": "^7.0.1",
     "ts-loader": "3",
     "babel-core": "^6.26.3",
diff --git a/src/useAsync.ts b/src/useAsync.ts
index c18df27314..aa0ecfe180 100644
--- a/src/useAsync.ts
+++ b/src/useAsync.ts
@@ -1,10 +1,18 @@
 import {useState, useEffect, useCallback} from 'react';
 
-export interface AsyncState<T> {
-  loading: boolean;
-  error?: Error | any;
-  value?: T;
+export type AsyncState<T> =
+| {
+  loading: true;
 }
+| {
+  loading: false;
+  error: Error;
+}
+| {
+  loading: false;
+  error?: undefined;
+  value: T;
+};
 
 const useAsync = <T>(fn: () => Promise<T>, args?) => {
   const [state, set] = useState<AsyncState<T>>({