feat: add useUpdateEffect hook

README.md

@@ -82,6 +82,7 @@
   - [`useLogger`](./docs/useLogger.md) — logs in console as component goes through life-cycles.
   - [`useMount`](./docs/useMount.md) — calls `mount` callbacks.
   - [`useUnmount`](./docs/useUnmount.md) — calls `unmount` callbacks.
+  - [`useUpdateEffect`](./docs/useUpdateEffect.md) — run an `effect` only on updates.
     <br/>
     <br/>
 - [**State**](./docs/State.md)

docs/useUpdateEffect.md

@@ -0,0 +1,35 @@
+# `useUpdateEffect`
+
+React effect hook that ignores the first invocation (e.g. on mount). The signature is exactly the same as the `useEffect` hook.
+
+
+## Usage
+
+```jsx
+import React from 'react'
+import {useUpdateEffect} from 'react-use';
+
+const Demo = () => {
+  const [count, setCount] = React.useState(0);
+  
+  React.useEffect(() => {
+    const interval = setInterval(() => {
+      setCount(count => count + 1)
+    }, 1000)
+    
+    return () => {
+      clearInterval(interval)
+    }
+  }, [])
+  
+  useUpdateEffect(() => {
+    console.log('count', count) // will only show 1 and beyond
+    
+    return () => { // *OPTIONAL*
+      // do something on unmount
+    }
+  }) // you can include deps array if necessary
+
+  return <div>Count: {count}</div>
+};
+```

src/__stories__/useUpdateEffect.story.tsx

@@ -0,0 +1,25 @@
+import {storiesOf} from '@storybook/react';
+import * as React from 'react';
+import {useUpdateEffect} from '..';
+
+const Demo = () => {
+  const [count, setCount] = React.useState(0)
+  const [didUpdate, setDidUpdate] = React.useState(false)
+  
+  useUpdateEffect(() => {
+    setDidUpdate(true)
+  }, [count])
+
+  return (
+    <div>
+      <button onClick={() => setCount(count => count + 1)}>Count: {count}</button>
+      <p>Updated: {didUpdate}</p>
+    </div>
+  );
+};
+
+storiesOf('useUpdateEffect', module)
+  .add('Docs', () => <ShowDocs md={require('../../docs/useUpdateEffect.md')} />)
+  .add('Demo', () =>
+    <Demo/>
+  )

src/index.ts

@@ -49,6 +49,7 @@ import useUpdate from './useUpdate';
 import useVideo from './useVideo';
 import useWindowSize from './useWindowSize';
 import useWait from './useWait';
+import useUpdateEffect from './useUpdateEffect'
 
 export {
   createMemo,
@@ -101,5 +102,6 @@ export {
   useUpdate,
   useVideo,
   useWindowSize,
-  useWait
+  useWait,
+  useUpdateEffect
 };

src/useUpdateEffect.ts

@@ -0,0 +1,16 @@
+import { useRef, useEffect } from 'react'
+
+const useUpdateEffect: typeof useEffect = (effect, deps) => {
+  const isInitialMount = useRef(true)
+
+  useEffect(
+    isInitialMount.current
+      ? () => {
+          isInitialMount.current = false
+        }
+      : effect,
+    deps
+  )
+}
+
+export default useUpdateEffect