Add usePrevious hook snippet

snippets/usePrevious.md

@@ -0,0 +1,36 @@
+---
+title: usePrevious
+tags: hooks,state,effect,intermediate
+---
+
+A hook that stores the previous state or props.
+
+- Create a custom hook that takes a `value`.
+- Use the `React.useRef()` hook to create a `ref` for the `value`.
+- Use the `React.useEffect()` hook to remember the latest `value`.
+
+```jsx
+const usePrevious = value => {
+  const ref = React.useRef();
+  React.useEffect(() => {
+    ref.current = value;
+  });
+  return ref.current;
+}
+```
+
+```jsx
+const Counter = () => {
+  const [value, setValue] = React.useState(0);
+  const lastValue = usePrevious(value);
+  
+  return (
+    <div>
+      <p>Current: {value} - Previous: {lastValue}</p>
+      <button onClick={() => setValue(value + 1)}>Increment</button>
+    </div>
+  );
+};
+
+ReactDOM.render(<Counter />, document.getElementById('root'));
+```