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Improve section useImperativeHandle #446

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25 changes: 14 additions & 11 deletions docs/basic/getting-started/hooks.md
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Expand Up @@ -215,22 +215,25 @@ function Foo() {

## useImperativeHandle

_We don't have much here, but this is from [a discussion in our issues](https://github.com/typescript-cheatsheets/react/issues/106). Please contribute if you have anything to add!_

It's normally used in combination with [`forwardRef`](https://github.com/typescript-cheatsheets/react/blob/main/README.md#forwardrefcreateref), and here's [an example from the React docs](https://reactjs.org/docs/hooks-reference.html#useimperativehandle) typed:
```tsx
type ListProps<ItemType> = {
items: ItemType[];
innerRef?: React.Ref<{ scrollToItem(item: ItemType): void }>;
};

function List<ItemType>(props: ListProps<ItemType>) {
useImperativeHandle(props.innerRef, () => ({
scrollToItem() {},
function FancyInput(props: {}, ref: React.Ref<{ focus: () => void }>) {
const inputRef = useRef<HTMLInputElement>(null);
useImperativeHandle(ref, () => ({
focus: () => {
inputRef.current?.focus();
},
}));
return null;
return <input ref={inputRef} />;
}
const Input = forwardRef<{ focus: () => void }, {}>(FancyInput);
```

### See also

- [A discussion in our issues](https://github.com/typescript-cheatsheets/react/issues/106)

## Custom Hooks

If you are returning an array in your Custom Hook, you will want to avoid type inference as TypeScript will infer a union type (when you actually want different types in each position of the array). Instead, use [TS 3.4 const assertions](https://devblogs.microsoft.com/typescript/announcing-typescript-3-4/#const-assertions):
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