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add useRef notes per #388 #389

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Jan 27, 2021
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add useRef notes per #388 #389

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add useRef notes per #388
swyxio Jan 26, 2021
781c0ad
Update docs/basic/getting-started/hooks.md
swyxio Jan 27, 2021
1b9c00e
Update docs/basic/getting-started/hooks.md
swyxio Jan 27, 2021
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13 changes: 9 additions & 4 deletions docs/basic/getting-started/hooks.md
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Original file line number Diff line number Diff line change
Expand Up @@ -130,10 +130,13 @@ When using `useRef`, you have two options when creating a ref container that doe

```ts
const ref1 = useRef<HTMLElement>(null!);
const ref2 = useRef<HTMLElement | null>(null);
const ref2 = useRef<HTMLElement>(null);
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There are two ref2 variables?

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good catch, i fixed

const ref3 = useRef<HTMLElement | null>(null);
```

The first option will make `ref1.current` read-only, and is intended to be passed in to built-in `ref` attributes that React will manage (because React handles setting the `current` value for you).
You can see the difference in [this playground](https://www.typescriptlang.org/play#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcARFDvmQNwCwAUI7hAHarwCCYYcAvHAAUASn4A+OAG9GjOHAD0CBLLnKGcxHABiwKBzgQwMYGxS4WUACbBWAczgwIcSxFwBXEFlYxkxtgDoVTQBJVmBjZAAbOAA3KLcsOAB3YEjogCNE1jc0-zgAGQBPG3tHOAAVQrAsAGVcKGAjOHTCuDdUErhWNgBabLSUVFQsWBNWA2qoX2hA9VU4AGFKXyx0AFk3H3TIxOwCOAB5dIArLHwgpHcoSm84MGJJmFbgdG74ZcsDVkjC2Y01f7yFQsdjvLAEACM-EwVBg-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-bfK05SrDA8mWVagHAbZeScOY0CjqUE6uOgqDaRAOSfKqOYgb8KiMaZ9GSeCEIMkyMVyUwRHWYc7nSvAgUQEk6AjMQXpReWyWGdFLHeBZHEuTCQEZT8xVwaV8BxZCzUWZQMDvuMghBHASJVnCWhTLYApiH1chIqgxpGeCfCSIxAC+Yj3o+8YvvgSLyNNOLjeBGhTTNdLzVJy3reGMBbTtrB7RoB3XbNBAneCsHLatcbPhdV3GrdB1WYhw3IKNZq-W2DCLYRO7QPAljgsgORcDwVJAA), thanks to [this discussion with @rajivpunjabi](https://github.com/typescript-cheatsheets/react/issues/388).

The first option will bypass nullchecks on `ref1.current`, and is intended to be passed in to built-in `ref` attributes that React will manage (because React handles setting the `current` value for you).

<details>
<summary>What is the <code>!</code> at the end of <code>null!</code>?</summary>
Expand All @@ -142,7 +145,7 @@ The first option will make `ref1.current` read-only, and is intended to be passe

```ts
function MyComponent() {
const ref1 = useRef<HTMLElement>(null!);
const ref1 = useRef<HTMLDivElement>(null!);
useEffect(() => {
doSomethingWith(ref1.current);
// TypeScript won't require null-check e.g. ref1 && ref1.current
Expand All @@ -153,7 +156,9 @@ function MyComponent() {

</details>

The second option will make `ref2.current` mutable, and is intended for "instance variables" that you manage yourself.
The second option will infer a `RefObject` instead of a `MutableRefObject`. This means there will be a type error ifyou try to assign to `ref2.current`.

The third option will make `ref3.current` mutable, and is intended for "instance variables" that you manage yourself.

```tsx
function TextInputWithFocusButton() {
Expand Down