Add useDefault hook

snippets/useDefault.md

@@ -0,0 +1,35 @@
+---
+title: useDefault
+tags: hooks,state,intermediate
+firstSeen: 2021-10-23T05:00:00-04:00
+---
+
+Creates a stateful value with a default fallback if it's `null` or `undefined`, and a function to update it.
+
+- Use the `useState()` hook to create stateful value.
+- Check if the value is either `null` or `undefined`.
+- Return the `defaultState` if it is, otherwise return the actual `value` state, alongside the `setValue` function.
+
+```jsx
+const useDefault = (defaultState, initialState) => {
+  const [value, setValue] = React.useState(initialState);
+  const isValueEmpty = value === undefined || value === null;
+  return [isValueEmpty ? defaultState : value, setValue];
+};
+```
+
+```jsx
+const UserCard = () => {
+  const [user, setUser] = useDefault({ name: 'Adam' }, { name: 'John' });
+
+  return (
+    <>
+      <div>User: {user.name}</div>
+      <input onChange={e => setUser({ name: e.target.value })} />
+      <button onClick={() => setUser(null)}>Clear</button>
+    </>
+  );
+};
+
+ReactDOM.render(<UserCard />, document.getElementById('root'));
+```