# Alpine composition

_Vue composition API for AlpineJS._

## Usage

### 1. Define the component

```ts
import { defineComponent, registerComponent } from 'alpine-composition';
import { setAlpine } from 'alpine-reactivity';

// If the Alpine package is NOT available globally under
// window.Alpine, set it here
setAlpine(Alpine);

// Define component similarly to defining Vue components
const Button = defineComponent({
  name: 'Button',

  // Props are defined the same way as with Vue
  props: {
    name: {
      type: String,
      required: true,
    },
    startCount: {
      type: Number,
      default: 0,
    },
  },

  // Instead of Alpine's init(), use setup()
  // - Props are passed down as reactive props, same as in Vue
  // - Second argument is the Alpine component instance.
  // - Third argument is reactivity API that is scoped to destroy references
  //   when the component is destroyed.
  // - Any additional args are inputs to `x-data`
  setup(props, vm, reactivity, ...args) {
    const { ref, toRefs, computed, watch, onBeforeUnmount } = reactivity;

    const { name, startCount } = toRefs(props);

    // Inside setup() you can use reactivity and composables
    const counter = ref(startCount.value);

    const { increaseCounter, disposeCounter } = useCounter(counter);

    const countFormatted = computed(() => {
      return `Clicked button ${name.name} ${counter.value} times!`
    });

    watch(counter, () => {
      // NOTE: `this` is undefined in `setup()`. Instead, use
      // the second argument `vm` to access the component instance.
      vm.$dispatch('clicked', counter.value);
    });

    const onClick = () => {
      increaseCounter();
    };

    // Instead of Alpine's `destroy()`, use `$onBeforeUnmount()`.
    // This behaves like Vue's `onBeforeUnmount` - it can be called
    // as many times as necessary.
    // At component's `destroy` event, all callbacks will be evaluated:
    onBeforeUnmount(() => {
      disposeCounter();
    });

    return {
      counter,
      countFormatted,
      onClick,
    };
  },
});
```

### 2. Register the component

This is where the magic happens. `registerComponent` is a wrapper for `Alpine.data`,
and it's thanks to this function that the component accepts props, has `setup` method,
and more.

```ts
import { registerComponent } from 'alpine-composition';

document.addEventListener('alpine:init', () => {
  registerComponent(Alpine, Button);
});
```

### 3. Use the component in the HTML

```html
<div x-data="{ inputValue: 10 }">

  <!--
    Use our component with `x-data` and pass props
    with `x-props`
  -->
  <div
    x-data="Button"
    x-props="{ startCount: inputValue, name: 'MyButton' }"
  >

    <!--
      Inside of the component, we can access ONLY values
      returned from `setup()`
    -->
    <span x-text="countFormatted.value"></span>
    <button @click="onClick">Click me!</button>

    <!-- You can even nest components -->
     <div x-data="Button" x-props="{ name: 'InnerButton' }">
      <span x-text="countFormatted.value"></span>
      <button @click="onClick">Click me too!</button>
     </div>

  </div>
</div>
```

## Installation

### Via CDN

```html
<script defer src="https://cdn.jsdelivr.net/npm/alpine-composition@0.x.x/dist/cdn.min.js"></script>
```

```js
const { defineComponent, registerComponent } = AlpineComposition;

const Button = defineComponent({
  name: 'Button',
  props: { ... },
  setup() { ... },
});
```

### Via NPM

```sh
npm install alpine-composition
```

```js
import { defineComponent, registerComponent } from 'alpine-composition';

const Button = defineComponent({
  name: 'Button',
  props: { ... },
  setup() { ... },
});
```

## Setup context and Magics

Inside of the `setup()` method, you can access the Alpine component instance
as the second argument. This instance has [all Alpine magics](https://alpinejs.dev/magics/el).

`alpine-composition` adds 8 more magics:

- `$name` - Name of the component. Readonly property.

- `$props` - Props passed to the component as reactive object.

- `$attrs` - HTML attributes (as object) of the element where the `x-data` was defined.

- `$options` - Component definition.

- `$emitsOptions` - Emits definition.

- `$initState` - Initial state, set via `data-x-init`, [see below](#initializing-component-state-from-html).

- `$emit` - Vue-like `emit()` method. Unlike `$dispatch`, `$emit` expects event handlers
to be set as props (e.g. `onClickButton` or `onClickButtonOnce` for event `'clickButton'`).
Thus, handlers for events emitted with `$emit()` must be explicitly defined on the component
that emits that event. In other words, the even does NOT bubble up. And when no event handler
is passed as a prop, the event is NOT sent.

  Similar to Vue, the `$emit` method has the event names and inputs autoamtically inferred from
  the component options when using TypeScript.

- `$onBeforeUnmount` - Equivalent of [Vue's `onBeforeUnmount`](https://vuejs.org/api/composition-api-lifecycle#onbeforeunmount).
Use this instead of Alpine's `destroy` hook.

```ts
import { defineComponent } from 'alpine-composition';

const Button = defineComponent({
  name: 'Button',
  setup(props, vm, reactivity) {
    const { ref, computed, watch, onBeforeUnmount } = reactivity;

    const nameEl = vm.$el.querySelector('input[name="name"]');
    
    console.log(vm.$name);

    onBeforeUnmount(() => {
      doUnregisterSomething();
    });

    const inputVal = ref('');

    watch(inputVal, (newVal, oldVal) => {
      // Send an event that can be captured with
      // `x-on:input` directive
      vm.$dispatch('input', newVal);

      // Send an event that can be captured with
      // `onInput` prop
      vm.$emit('input', newVal);
    }, { immediate: true });
  },
});
```

## Component isolation

To make the Alpine components behave more like Vue, the components created by
`registerComponent` are automatically isolated from outer components. This can
be disabled by setting `isolated: false` on the component.

Normally when you have an Alpine components like so:
```html
<div x-data="{ hello: 'world' }" id="outer"> 
  <div x-data="{ foo: 'bar' }" id="inner">
  </div>
</div>
```

Then the inner component has access to the scope (data) from the outer components:

```html
<div x-data="{ hello: 'world' }" id="outer"> 
  <div x-data="{ foo: 'bar' }" id="inner" x-text="hello + ' ' + foo">
    <!-- Renders: 'world bar' -->
  </div>
</div>
```

However, to mimic Vue API, we need to explicitly pass down data as props.
Because of this, components don't have access to the outer scopes:

```html
<div x-data="{ hello: 'world' }" id="outer"> 
  <div x-data="{ foo: 'bar' }" x-props="{ hello2: hello }" id="inner" x-text="hello2 + ' ' + foo">
    <!-- Renders: 'world bar' -->
  </div>
</div>
```

To allow access to outer scopes, set `isolated: false` on the component definition:

```ts
const Button = defineComponent({
  name: 'Button',
  props: { ... },
  setup() { ... },

  isolated: false,
});
```

## Initializing component state from HTML

Sometimes, you may want to initialize a component to a certain state,
without exposing the inner state as props.

Imagine we have a button component, and we want to set the button width
at page load. We want different buttons to have different width,
but we want the width to remain constant for the rest of its existence.

For this `alpine-composition` allows to set the internal component state
from JSON, passed to the component as `data-x-init` attribute:

```ts
import { defineComponent, registerComponent } from 'alpine-composition';

const Button = defineComponent({
  name: 'Button',

  setup(props, vm) {
    // Either use the value defined outside, or default to '20px'
    const buttonWidth = vm.$initState.buttonWidth || '20px';
    const buttonStyle = `width: ${buttonWidth}; height: 40px; background: yellow;`;

    return {
      buttonStyle,
    };
  },
});
```

Where does the value `vm.$initState.buttonWidth` come from? This is taken from the
component's initial state. See below:

```html
<button x-data="Button" data-x-init='{ "buttonWidth": "100%" }' :style="buttonStyle">
  Clock Me!
</button>
```

You can change which data key is used for initial data by setting the `initKey` option.

`initKey` should be a valid HTML attribute - it should be lowercase, and contain only
letters and dashes.

`initKey` will be prefixed with `x-` to avoid conflicts.

So, in the example below, we can define the initial state via the `data-x-my-init`
attribute by setting the `initKey` option to `my-init`:

```ts
const Button = defineComponent({
  name: 'Button',
  initKey: 'my-init',
  setup(props, vm) { ... },
});
```

```html
<button x-data="Button" data-x-my-init='{ "buttonWidth": "100%" }' ...>
  Clock Me!
</button>
```

## Extending

`alpine-composition` comes with a plugin system that allows you to modify the Alpine instance
for each component registered with the respective `registerComponent` function.

The example below is taken from Alpinui. Here, we defined a plugin for new magic
attribute `$aliasName` accessible inside the `setup()` method. `$aliasName` returns
the value of `aliasName` component option.

```ts
import {
  createAlpineComposition,
  defineComponent,
  type Data,
  type PluginFn,
} from 'alpine-composition';

import type { Alpine as AlpineType } from 'alpinejs';
import type { Magics } from 'alpinejs';

export interface CreateAlpinuiOptions {
  components?: Record<string, any>;
}

// Extend the types, so we get type hints for `vm.$aliasName` 
// and can specify `aliasName` on the component definition.
declare module 'alpine-composition' {
  interface AlpineInstance <P extends Data> extends Magics<P> {
    $aliasName?: string;
  }

  interface ComponentOptions <T extends Data, P extends Data> {
    aliasName?: string;
  }
}

// Alpinui adds `$aliasName` to the Alpine components
// Plugins receive the VM as the first arg, and context as second.
const aliasNamePlugin: PluginFn<Data, Data> = (vm, { options }) => {
  const { aliasName } = options;

  Object.defineProperty(vm, '$aliasName', {
    get() {
      return aliasName;
    },
  });
};

/** Register Alpinui components with Alpine */
export function createAlpinui(
  options: CreateAlpinuiOptions = {},
) {
  const { components = {} } = options;

  // We pass the plugins to `createAlpineComposition`.
  // This returns an instance of `registerComponent` function.
  // This behaves the same as the module-level `registerComponent`,
  // except it also calls our plugins.
  const { registerComponent } = createAlpineComposition({
    plugins: [
      aliasNamePlugin,
    ],
  });

  // Alpinui allows users to provide their own instance of Alpine
  // via install()
  const install = (Alpine: AlpineType) => {
    for (const key in components) {
      registerComponent(Alpine, components[key]);
    }
  };

  return {
    install,
    registerComponent,
  };
}
```

After we have created `createAlpinui`, we can register components with it like so:

```ts
import { defineComponent } from 'alpine-composition';

const Button = defineComponent({
  name: 'Button',
  props: { ... },
  setup() { ... },
  aliasName: 'ButtonAlias',
});

const alpinui = createAlpinui({
  components: { ... },
});

// NOTE: We use the newly created `registerComponent`,
// NOT the one from `alpine-composition`
alpinui.registerComponent(Alpine, Button);
```

## Reference

[See the docs](./docs/typedoc/modules.md)