# Mixins, Styling, and Events

## What This Covers

How to attach behavior, styles, and DOM-aware setup to host elements with `mix`. Read this when the task involves:

- DOM event handling with `on(...)`
- Static styling with `css(...)` and dynamic styling with `style`
- Imperative DOM access via `ref(...)`
- Navigation behavior on non-anchor elements with `link(...)`
- Native click, pointer, and keyboard behavior with `on(...)`, plus attributes with `attrs(...)`
- Element-level animation mixins from `remix/ui/animation`

For richer animation work (springs, tweens, layout transitions), see `animate-elements.md`. For authoring custom mixins, see `create-mixins.md`. For component lifecycle and updates, see `component-model.md`.

Compose behavior on host elements with `mix`. Pass a single mixin directly (`mix={on(...)}`), or an array when composing multiple mixins (`mix={[css(...), on(...)]}`). Core mixins are imported from `remix/ui`; animation mixins are imported from `remix/ui/animation`.

## `on(type, handler, capture?)`

Attaches a typed DOM event handler. The handler receives the event and an `AbortSignal` that aborts when the handler is re-entered or the component is removed — this prevents race conditions:

```tsx
<input
  mix={on('input', async (event, signal) => {
    let query = event.currentTarget.value
    loading = true
    handle.update()

    let response = await fetch(`/search?q=${query}`, { signal })
    let data = await response.json()
    if (signal.aborted) return

    results = data.results
    loading = false
    handle.update()
  })}
/>
```

Multiple events on the same element:

```tsx
<form
  mix={on('submit', (event) => {
      event.preventDefault()
      let formData = new FormData(event.currentTarget)
    })}
>
```

## `css(styles)`

Applies generated class names for CSS object styles. Produces static CSS rules inserted into the document. Supports pseudo-selectors, pseudo-elements, attribute selectors, descendant selectors, and media queries using `&` to reference the current element:

```tsx
<button
  mix={css({
    color: 'white',
    backgroundColor: 'blue',
    padding: '12px 24px',
    borderRadius: '4px',
    border: 'none',
    cursor: 'pointer',
    '&:hover': { backgroundColor: 'darkblue' },
    '&:active': { transform: 'scale(0.98)' },
    '&:disabled': { opacity: 0.5, cursor: 'not-allowed' },
    '& .title': { fontSize: '20px', fontWeight: 'bold' },
    '@media (max-width: 768px)': { width: '100%' },
  })}
/>
```

### `css(...)` vs `style` prop

Use `css(...)` for static styles, selectors, and media queries. Use `style` for dynamic values that change often. Prefer CSS nested selectors for parent-state-affects-children over managing hover/focus state in JavaScript:

```tsx
<div
  mix={css({
    backgroundColor: 'blue', // static
    '&:hover': { '& .title': { color: 'blue' } }, // parent hover → child
  })}
  style={{ width: `${progress}%` }} // dynamic
/>
```

## `ref(callback)`

Calls a callback when an element is inserted. The callback receives the DOM node and an `AbortSignal` that aborts when the element is removed:

```tsx
<input mix={ref((node) => node.focus())} />

<div mix={ref((node, signal) => {
  let observer = new ResizeObserver((entries) => {
    dimensions.width = Math.round(entries[0].contentRect.width)
    handle.update()
  })
  observer.observe(node)
  signal.addEventListener('abort', () => observer.disconnect())
})} />
```

The `ref` callback runs once when the element is first rendered, not on every update.

## `link(href, options?)`

Adds client-side navigation behavior to any element. Makes non-anchor elements behave like Remix navigation links:

```tsx
<article mix={link('/courses/intro')}>
  <h3>Introduction</h3>
</article>
```

Options match `NavigationOptions`: `src`, `target`, `history` (`'push' | 'replace'`), `resetScroll`.

On a native anchor, the `history` option renders the corresponding `rmx-history="push|replace"` attribute so the enhanced navigation uses the same history behavior.

## Native press and keyboard interactions

Use native DOM events directly with `on(...)`. For buttons and links, `click` already includes keyboard activation when the element has the right semantics:

```tsx
<button mix={on('click', () => doAction())}>Action</button>
```

For gesture-specific behavior, compose the pointer or keyboard events the interaction actually needs:

```tsx
<button
  mix={[
    on('pointerdown', (event) => {
      event.currentTarget.setPointerCapture(event.pointerId)
    }),
    on('pointerup', () => doAction()),
  ]}
>
  Action
</button>

<div
  tabIndex={0}
  mix={on('keydown', (event) => {
      if (event.key === 'Escape') close()
      if (event.key === 'Enter' || event.key === ' ') doAction()
    })}
/>
```

## `attrs()`

Sets HTML attributes through the mixin system.

## Animation Mixins

### `animateEntrance(config)`

Animates an element when it is inserted into the DOM. Config specifies the **starting** style:

```tsx
<div mix={animateEntrance({ opacity: 0, transform: 'translateY(8px)', duration: 180 })} />
```

### `animateExit(config)`

Animates an element when it is removed. Config specifies the **ending** style. The element is kept in the DOM until the animation completes:

```tsx
{
  isVisible && (
    <div
      key="panel"
      mix={[
        animateEntrance({ opacity: 0, transform: 'scale(0.98)', ...spring('smooth') }),
        animateExit({ opacity: 0, duration: 120, easing: 'ease-in' }),
      ]}
    />
  )
}
```

### `animateLayout(config?)`

Animates layout changes (position/size) using FLIP-style transforms:

```tsx
{
  items.map((item) => (
    <li key={item.id} mix={animateLayout({ duration: 220, easing: 'ease-out' })} />
  ))
}
```

Options: `duration` (default 200ms), `easing` (default spring snappy), `size` (boolean, default true — include scale projection for size changes).

Always key elements you expect to animate. Use `...spring(preset)` to spread `duration` and `easing` into any animation config.