# useTransition

Provides the ability to apply CSS transitions to a floating
element, including correct handling of "placement-aware"
transitions.

There are two different hooks you can use:

- [`useTransitionStyles`](/docs/useTransition#usetransitionstyles)
  — a high level wrapper around `useTransitionStatus` that
  returns computed styles for you. This is simpler and can handle
  the majority of use cases.
- [`useTransitionStatus`](/docs/useTransition#usetransitionstatus)
  — a low level hook that returns a status string to compute the
  styles yourself.

## useTransitionStyles

This hook provides computed inline styles that you can spread
into the `style{:.keyword}` prop for a floating element.

This hook is a standalone hook that accepts the
`context{:.const}` object returned from `useFloating(){:js}`:

```js /context/
function App() {
  const {context} = useFloating();
  const {isMounted, styles} = useTransitionStyles(context);

  return (
    isMounted && (
      <div
        style={{
          // Transition styles
          ...styles,
        }}
      >
        Tooltip
      </div>
    )
  );
}
```

- `isMounted{:.const}` is a boolean that determines whether or
  not the floating element is mounted on the screen, which allows
  for unmounting animations to play. This replaces the
  `open{:.const}` state variable.
- `styles{:.const}` is an object of inline transition styles
  (`React.CSSProperties{:ts}`).

The hook defaults to a basic opacity fade transition with a
duration of 250ms.

## useTransitionStyles Props

```ts
interface UseTransitionStylesProps {
  duration?: number | Partial<{open: number; close: number}>;
  initial?: CSSStylesProperty;
  open?: CSSStylesProperty;
  close?: CSSStylesProperty;
  common?: CSSStylesProperty;
}
```

### duration

default: `250{:js}`

Specifies the length of the transition in ms.

```js
const {isMounted, styles} = useTransitionStyles(context, {
  // Configure both open and close durations:
  duration: 200,

  // Or, configure open and close durations separately:
  duration: {
    open: 200,
    close: 100,
  },
});
```

### initial

default: `{opacity: 0}`

Specifies the initial styles of the floating element:

```js
const {isMounted, styles} = useTransitionStyles(context, {
  initial: {
    opacity: 0,
    transform: 'scale(0.8)',
  },
});
```

This will implicitly transition to empty strings for each value
(their defaults of `opacity: 1{:sass}` and
`transform: scale(1){:sass}`).

For placement-aware styles, you can define a function:

```js
const {isMounted, styles} = useTransitionStyles(context, {
  initial: ({side}) => ({
    transform:
      side === 'top' || side === 'bottom'
        ? 'scaleY(0.5)'
        : 'scaleX(0.5)',
  }),
});
```

The function takes the following parameters:

```ts
interface Params {
  side: Side;
  placement: Placement;
}
```

- `side{:.objectKey}` represents a physical side — with the vast
  majority of transitions, you'll likely only need to be
  concerned about the side.
- `placement{:.objectKey}` represents the whole placement string
  in cases where you want to also change the transition based on
  the alignment.

### close

default: `undefined{:js}`

By default, transitions are symmetric, but if you want an
asymmetric transition, then you can specify `close` styles:

```js
const {isMounted, styles} = useTransitionStyles(context, {
  close: {
    opacity: 0,
    transform: 'scale(2)',
  },
  // or, for side-aware styles:
  close: ({side}) => ({
    opacity: 0,
    transform:
      side === 'top' || side === 'bottom'
        ? 'scaleY(2)'
        : 'scaleX(2)',
  }),
});
```

<Notice>
  You don't need to specify this unless you want an asymmetric
  transition.
</Notice>

### open

default: `undefined{:js}`

If you want the open state to transition to a non-default style,
`open` styles can be specified:

```js
const {isMounted, styles} = useTransitionStyles(context, {
  open: {
    transform: 'scale(1.1)',
  },
  // or, for side-aware styles:
  open: ({side}) => ({
    transform:
      side === 'top' || side === 'bottom'
        ? 'scaleY(1.1)'
        : 'scaleX(1.1)',
  }),
});
```

### common

default: `undefined{:js}`

If a style is common across all states, then this option can be
specified. For instance, a transform origin should be shared:

```js
const {isMounted, styles} = useTransitionStyles(context, {
  common: {
    transformOrigin: 'bottom',
  },
  // or, for side-aware styles:
  common: ({side}) => ({
    transformOrigin: {
      top: 'bottom',
      bottom: 'top',
      left: 'right',
      right: 'left',
    }[side],
  }),
});
```

### Scale transforms

When animating the floating element's scale, it looks best if the
floating element's `transformOrigin{:.objectKey}` is at the tip
of the arrow. The `arrow` middleware provides data to achieve
this.

[View on CodeSandbox](https://codesandbox.io/s/floating-ui-react-scale-transform-origin-qv0t1c?file=/src/App.tsx)

## useTransitionStatus

This hook provides a `status{:.const}` string that determines if
the floating element is in one of four states:

```ts
type Status = 'unmounted' | 'initial' | 'open' | 'close';
```

The floating element cycles through the order as seen below:

```text
unmounted -> initial -> open -> close -> unmounted
```

This hook is a standalone hook that accepts the
`context{:.const}` object returned from `useFloating(){:js}`:

```js /context/
function App() {
  const {context, placement} = useFloating();
  const {isMounted, status} = useTransitionStatus(context);

  return (
    isMounted && (
      <div id="floating" data-status={status}>
        Tooltip
      </div>
    )
  );
}
```

- `isMounted{:.const}` is a boolean that determines whether or
  not the floating element is mounted on the screen, which allows
  for unmounting animations to play. This replaces the
  `open{:.const}` state variable.
- `status{:.const}` is the status string (`Status{:.class}`).

Above, we apply a `data-status{:.keyword}` attribute to the
floating element. This can be used to target the transition
status in our CSS.

To define an opacity fade CSS transition:

```css
#floating {
  transition-property: opacity;
}
#floating[data-status='open'],
#floating[data-status='close'] {
  transition-duration: 250ms;
}
#floating[data-status='initial'],
#floating[data-status='close'] {
  opacity: 0;
}
```

- `transition-property: opacity{:sass}` is applied to **all**
  states. This allows the transition to be interruptible.

The statuses map to the following:

- `'unmounted'{:js}` indicates the element is unmounted from the
  screen. No transitions or styles need to be applied in this
  state.
- `'initial'{:js}` indicates the initial styles of the floating
  element as soon as it has been inserted into the DOM.
- `'open'{:js}` indicates the floating element is in the open
  state (1 frame after insertion) and begins transitioning in.
- `'close'{:js}` indicates the floating element is in the close
  state and begins transitioning out.

The transition duration must match the `duration{:.objectKey}`
option passed to the hook.

### Asymmetric transitions

```css
#floating {
  transition-property: opacity, transform;
}
#floating[data-status='initial'] {
  opacity: 0;
  transform: scale(0);
}
#floating[data-status='open'] {
  opacity: 1;
  transform: scale(1);
  transition-duration: 250ms;
}
#floating[data-status='close'] {
  opacity: 0;
  transform: scale(2);
  transition-duration: 250ms;
}
```

### Placement-aware transitions

```js /placement/
const {context, placement} = useFloating();
const {isMounted, status} = useTransitionStatus(context);

return (
  isMounted && (
    <div
      id="floating"
      data-placement={placement}
      data-status={status}
    >
      Tooltip
    </div>
  )
);
```

```css
#floating {
  transition-property: opacity, transform;
}
#floating[data-status='open'],
#floating[data-status='close'] {
  transition-duration: 250ms;
}
#floating[data-status='initial'],
#floating[data-status='close'] {
  opacity: 0;
}
#floating[data-status='initial'][data-placement^='top'],
#floating[data-status='close'][data-placement^='top'] {
  transform: translateY(5px);
}
#floating[data-status='initial'][data-placement^='bottom'],
#floating[data-status='close'][data-placement^='bottom'] {
  transform: translateY(-5px);
}
#floating[data-status='initial'][data-placement^='left'],
#floating[data-status='close'][data-placement^='left'] {
  transform: translateX(5px);
}
#floating[data-status='initial'][data-placement^='right'],
#floating[data-status='close'][data-placement^='right'] {
  transform: translateX(-5px);
}
```

## useTransitionStatus Props

```ts
interface UseTransitionStatusProps {
  duration?: number | Partial<{open: number; close: number}>;
}
```

### duration

default: `250{:js}`

Specifies the length of the transition in ms.

```js
const {isMounted, status} = useTransitionStatus(context, {
  // Configure both open and close durations:
  duration: 200,

  // Or, configure open and close durations separately:
  duration: {
    open: 200,
    close: 100,
  },
});
```
