1# `useSelector()` hook
2
3With `useSelector` React hook you specify a selector function, which will pick specific
4data from the state. *Your component will update only when that specific part of the state changes.*
5
6```tsx
7const selector = state => state.isDarkMode;
8const Demo = () => {
9  const isDarkMode = useSelector(selector);
10  return <div>{isDarkMode ? '��' : '☀️'}</div>;
11};
12```
13
14As an optional second argument for `useSelector` you can provide a `comparator` function, which
15compares currently selected value with the previous and your component will re-render only if
16`comparator` returns `true`. By default it uses [`fast-deep-equal`](https://github.com/epoberezkin/fast-deep-equal).
17
18```
19useSelector(selector, comparator?)
20```
21