diff --git a/docs/basic/getting-started/hooks.md b/docs/basic/getting-started/hooks.md
index 0a6d0f3a..29ecc4d2 100644
--- a/docs/basic/getting-started/hooks.md
+++ b/docs/basic/getting-started/hooks.md
@@ -137,65 +137,82 @@ function DelayedEffect(props: { timerMs: number }) {
## useRef
-When using `useRef`, you have two options when creating a ref container that does not have an initial value:
+In TypeScript, `useRef` returns a reference that is either [read-only](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/abd69803c1b710db58d511f4544ec1b70bc9077c/types/react/v16/index.d.ts#L1025-L1039) or [mutable](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/abd69803c1b710db58d511f4544ec1b70bc9077c/types/react/v16/index.d.ts#L1012-L1023), depends on whether your type argument fully covers the initial value or not. Choose one that suits your use case.
-```ts
-const ref1 = useRef<HTMLElement>(null!);
-const ref2 = useRef<HTMLElement>(null);
-const ref3 = useRef<HTMLElement | null>(null);
-```
+### Option 1: DOM element ref
-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).
+**[To access a DOM element](https://reactjs.org/docs/refs-and-the-dom.html):** provide only the element type as argument, and use `null` as initial value. In this case, the returned reference will have a read-only `.current` that is managed by React. TypeScript expects you to give this ref to an element's `ref` prop:
-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>
-
-`null!` is a non-null assertion operator (the `!`). It asserts that any expression before it is not `null` or `undefined`, so if you have `useRef<HTMLElement>(null!)` it means that you're instantiating the ref with a current value of `null` but lying to TypeScript that it's not `null`.
-
-```ts
-function MyComponent() {
- const ref1 = useRef<HTMLDivElement>(null!);
+```tsx
+function Foo() {
+ // - If possible, prefer as specific as possible. For example, HTMLDivElement
+ // is better than HTMLElement and way better than Element.
+ // - Technical-wise, this returns RefObject<HTMLDivElement>
+ const divRef = useRef<HTMLDivElement>(null);
+
useEffect(() => {
- doSomethingWith(ref1.current);
- // TypeScript won't require null-check e.g. ref1 && ref1.current
+ // Note that ref.current may be null. This is expected, because you may
+ // conditionally render the ref-ed element, or you may forgot to assign it
+ if (divRef.current) throw Error("divRef is not assigned");
+
+ // Now divRef.current is sure to be HTMLDivElement
+ doSomethingWith(divRef.current);
});
- return <div ref={ref1}> etc </div>;
+
+ // Give the ref to an element so React can manage it for you
+ return <div ref={divRef}>etc</div>;
}
```
+If you are sure that `divRef.current` will never be null, it is also possible to use the non-null assertion operator `!`:
+
+```
+const divRef = useRef<HTMLDivElement>(null!);
+// Later... No need to check if it is null
+doSomethingWith(divRef.current);
+```
+
+Note that you are opting out of type safety here - you will have a runtime error if you forget to assign the ref to an element in the render, or if the ref-ed element is conditionally rendered.
+
+<details>
+<summary>
+
+ Tip: Choosing which `HTMLElement` to use
+
+</summary>
+
+
+Refs demand specificity - it is not enough to just specify any old `HTMLElement`. If you don't know the name of the element type you need, you can check [lib.dom.ts](https://github.com/microsoft/TypeScript/blob/v3.9.5/lib/lib.dom.d.ts#L19224-L19343) or make an intentional type error and let the language service tell you:
+
+
+
</details>
-The second option will infer a `RefObject` instead of a `MutableRefObject`. This means there will be a type error if you try to assign to `ref2.current`.
-The third option will make `ref3.current` mutable, and is intended for "instance variables" that you manage yourself.
+### Option 2: Mutable value ref
+
+**[To have a mutable value](https://reactjs.org/docs/hooks-faq.html#is-there-something-like-instance-variables):** provide the type you want, and make sure the initial value fully belongs to that type:
```tsx
-function TextInputWithFocusButton() {
- // initialise with null, but tell TypeScript we are looking for an HTMLInputElement
- const inputEl = React.useRef<HTMLInputElement>(null);
- const onButtonClick = () => {
- // strict null checks need us to check if inputEl and current exist.
- // but once current exists, it is of type HTMLInputElement, thus it
- // has the method focus! ✅
- if (inputEl && inputEl.current) {
- inputEl.current.focus();
- }
- };
- return (
- <>
- {/* in addition, inputEl only can be used with input elements. Yay! */}
- <input ref={inputEl} type="text" />
- <button onClick={onButtonClick}>Focus the input</button>
- </>
- );
+function Foo() {
+ // Technical-wise, this returns MutableRefObject<number | null>
+ const intervalRef = useRef<number | null>(null);
+
+ // You manage the ref yourself (that's why it's called MutableRefObject!)
+ useEffect(() => {
+ intervalRef.current = setInterval(...);
+ return () => clearInterval(intervalRef.current);
+ }, []);
+
+ // The ref is not passed to any element's "ref" prop
+ return <button onClick={/* clearInterval the ref */}>Cancel timer</button>;
}
```
-[View in the TypeScript Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgIilQ3wFgAoCzAVwDsNgJa4AVJADxgElaxqYA6sBgALAGIQ01AM4AhfjCYAKAJRwA3hThwA9DrjBaw4CgA2waUjgB3YSLi1qp0wBo4AI35wYSZ6wCeYEgAymhQwGDw1lYoRHCmEBAA1oYA5nCY0HAozAASLACyADI8fDAAoqZIIEi0MFpwaEzS8IZllXAAvIjEMAB0MkjImAA8+cWl-JXVtTAAfEqOzioA3A1NtC1wTPIwirQAwuZoSV1wql1zGg3aenAt4RgOTqaNIkgn0g5ISAAmcDJvBA3h9TsBMAZeFNXjl-lIoEQ6nAOBZ+jddPpPPAmGgrPDEfAUS1pG5hAYvhAITBAlZxiUoRUqjU6m5RIDhOi7iIUF9RFYaqIIP9MlJpABCOCAUHJ0eDzm1oXAAGSKyHtUx9fGzNSacjaPWq6Ea6gI2Z9EUyVRrXV6gC+DRtVu0RBgxuYSnRIzm6O06h0ACpIdlfr9jExSQyOkxTP5GjkPFZBv9bKIDYSmbNpH04ABNFD+CV+nR2636kby+BETCddTlyo27w0zr4HycfC6L0lvUjLH7baHY5Jas7BRMI7AE42uYSUXed6pkY6HtMDulnQruCrCg2oA)
+### See also
-example from [Stefan Baumgartner](https://fettblog.eu/typescript-react/hooks/#useref)
+- [Related issue by @rajivpunjabi](https://github.com/typescript-cheatsheets/react/issues/388) - [Playground](https://www.typescriptlang.org/play#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcARFDvmQNwCwAUI7hAHarwCCYYcAvHAAUASn4A+OAG9GjOHAD0CBLLnKGcxHABiwKBzgQwMYGxS4WUACbBWAczgwIcSxFwBXEFlYxkxtgDoVTQBJVmBjZAAbOAA3KLcsOAB3YEjogCNE1jc0-zgAGQBPG3tHOAAVQrAsAGVcKGAjOHTCuDdUErhWNgBabLSUVFQsWBNWA2qoX2hA9VU4AGFKXyx0AFk3H3TIxOwCOAB5dIArLHwgpHcoSm84MGJJmFbgdG74ZcsDVkjC2Y01f7yFQsdjvLAEACM-EwVBg-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-bfK05SrDA8mWVagHAbZeScOY0CjqUE6uOgqDaRAOSfKqOYgb8KiMaZ9GSeCEIMkyMVyUwRHWYc7nSvAgUQEk6AjMQXpReWyWGdFLHeBZHEuTCQEZT8xVwaV8BxZCzUWZQMDvuMghBHASJVnCWhTLYApiH1chIqgxpGeCfCSIxAC+Yj3o+8YvvgSLyNNOLjeBGhTTNdLzVJy3reGMBbTtrB7RoB3XbNBAneCsHLatcbPhdV3GrdB1WYhw3IKNZq-W2DCLYRO7QPAljgsgORcDwVJAA)
+- [Example from Stefan Baumgartner](https://fettblog.eu/typescript-react/hooks/#useref) - [Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgIilQ3wFgAoCzAVwDsNgJa4AVJADxgElaxqYA6sBgALAGIQ01AM4AhfjCYAKAJRwA3hThwA9DrjBaw4CgA2waUjgB3YSLi1qp0wBo4AI35wYSZ6wCeYEgAymhQwGDw1lYoRHCmEBAA1oYA5nCY0HAozAASLACyADI8fDAAoqZIIEi0MFpwaEzS8IZllXAAvIjEMAB0MkjImAA8+cWl-JXVtTAAfEqOzioA3A1NtC1wTPIwirQAwuZoSV1wql1zGg3aenAt4RgOTqaNIkgn0g5ISAAmcDJvBA3h9TsBMAZeFNXjl-lIoEQ6nAOBZ+jddPpPPAmGgrPDEfAUS1pG5hAYvhAITBAlZxiUoRUqjU6m5RIDhOi7iIUF9RFYaqIIP9MlJpABCOCAUHJ0eDzm1oXAAGSKyHtUx9fGzNSacjaPWq6Ea6gI2Z9EUyVRrXV6gC+DRtVu0RBgxuYSnRIzm6O06h0ACpIdlfr9jExSQyOkxTP5GjkPFZBv9bKIDYSmbNpH04ABNFD+CV+nR2636kby+BETCddTlyo27w0zr4HycfC6L0lvUjLH7baHY5Jas7BRMI7AE42uYSUXed6pkY6HtMDulnQruCrCg2oA)
## useImperativeHandle