npm package: @kt3k/capsule
Description: Event-driven DOM programming in a new style
Latest version: 0.6.0

<img src="https://raw.githubusercontent.com/capsidjs/capsule/master/capsule-logo.svg" width="70" alt="capsule" />

# Capsule v0.6.0

[![ci](https://github.com/capsidjs/capsule/actions/workflows/ci.yml/badge.svg)](https://github.com/capsidjs/capsule/actions/workflows/ci.yml)

> Event-driven DOM programming in a new style

# Features

- Supports **event-driven** style of frontend programming in a **new way**.
- Supports **event delegation** and **outside events** out of the box.
- **Lightweight** library.
  [**1.25 kiB**](https://raw.githubusercontent.com/capsidjs/capsule/v0.6.0/dist.min.js)
  gzipped. **No dependencies**. **No build** steps.
- Uses **plain JavaScript** and **plain HTML**, requires **No special syntax**.
- **TypeScript** friendly.

[See live examples](https://capsule.deno.dev/)

# Motivation

Virtual DOM frameworks are good for many use cases, but sometimes they are
overkill for the use cases where you only need a little bit of event handlers
and dom modifications.

This `capsule` library explores the new way of simple event-driven DOM
programming without virtual dom.

# Slogans

- Local query is good. Global query is bad.
- Define behaviors based on HTML classes.
- Use pubsub when making remote effect.

## Local query is good. Global query is bad

When people use jQuery, they often do:

```js
$(".some-class").each(function () {
  $(this).on("some-event", () => {
    $(".some-target").each(function () {
      // some effects on this element
    });
  });
});
```

This is very common pattern, and this is very bad.

The above code can been seen as a behavior of `.some-class` elements, and they
use global query `$(".some-target")`. Because they use global query here, they
depend on the entire DOM tree of the page. If the page change anything in it,
the behavior of the above code can potentially be changed.

This is so unpredictable because any change in the page can affect the behavior
of the above class. You can predict what happens with the above code only when
you understand every details of the entire application, and that's often
impossible when the application is large size, and multiple people working on
that app.

So how to fix this? We recommend you should use **local** queries.

Let's see this example:

```js
$(".some-class").each(function () {
  $(this).on("some-event", () => {
    $(this).find(".some-target").each(function () {
      // some effects on this element
    });
  });
});
```

The difference is `$(this).find(".some-target")` part. This selects the elements
only under each `.some-class` element. So this code only depends on the elements
inside it, which means there is no global dependencies here.

`capsule` enforces this pattern by providing `query` function to event handlers
which only finds elements under the given element.

```js
const { on } = component("some-class");

on.click = ({ query }) => {
  query(".some-target").textContent = "clicked";
};
```

Here `query` is the alias of `el.querySelector` and it finds `.some-target` only
under it. So the dependency is **local** here.

## Define behaviors based on HTML classes

From our observation, skilled jQuery developers always define DOM behaviors
based on HTML classes.

We borrowed this pattern, and `capsule` allows you to define behavior only based
on HTML classes, not random combination of query selectors.

```html
<div class="hello">John Doe</div>
```

```js
const { on } = component("hello");

on.__mount__ = () => {
  alert(`Hello, I'm ${el.textContext}!`); // Alerts "Hello, I'm John Doe!"
};
```

## Use pubsub when making remote effect

We generally recommend using only local queries, but how to make effects to the
remote elements?

We reommend using pubsub pattern here. By using this pattern, you can decouple
those affecting and affected elements. If you decouple those elements, you can
test those components independently by using events as I/O of those components.

`capsule` library provides `pub` and `sub` APIs for encouraging this pattern.

```js
const EVENT = "my-event";
{
  const { on } = component("publisher");

  on.click = ({ pub }) => {
    pub(EVENT);
  };
}

{
  const { on, sub } = component("subscriber");

  sub(EVENT);

  on[EVENT] = () => {
    alert(`Got ${EVENT}!`);
  };
}
```

Note: `capsule` uses DOM Event as event payload, and `sub:EVENT` HTML class as
registration to the event. When `pub(EVENT)` is called the CustomEvent of
`EVENT` type are dispatched to the elements which have `sub:EVENT` class.

## TodoMVC

TodoMVC implementation is also available
[here](https://github.com/capsidjs/capsule-todomvc).

## Live examples

See [the live demos](https://capsule.deno.dev/).

# Install

Vanilla js (ES Module):

```html
<script type="module">
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";
// ... your code ...
</script>
```

Vanilla js (Legacy script tag):

```html
<script src="https://deno.land/x/capsule@v0.6.0/loader.js"></script>
<script>
capsuleLoader.then((capsule) => {
  const { component } = capsule;
  // ... your code ...
});
</script>
```

Deno:

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/mod.ts";
```

Via npm:

```
npm install @kt3k/capsule
```

and

```js
import { component } from "@kt3k/capsule";
```

# Examples

Mirrors input value of `<input>` element to another dom.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const { on } = component("mirroring");

on.input = ({ query }) => {
  query(".src").textContent = query(".dest").value;
};
```

Pubsub.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const EVENT = "my-event";

{
  const { on } = component("pub-element");

  on.click = ({ pub }) => {
    pub(EVENT, { hello: "world!" });
  };
}

{
  const { on, sub } = component("sub-element");

  sub(EVENT);

  on[EVENT] = ({ e }) => {
    console.log(e.detail.hello); // => world!
  };
}
```

Mount hooks.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const { on } = component("my-component");

// __mount__ handler is called when the component mounts to the elements.
on.__mount__ = () => {
  console.log("hello, I'm mounted");
};
```

Prevent default, stop propagation.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const { on } = component("my-component");

on.click = ({ e }) => {
  // e is the native event object.
  // You can call methods of Event object
  e.stopPropagation();
  e.preventDefault();
  console.log("hello, I'm mounted");
};
```

Event delegation. You can assign handlers to `on(selector).event` to use
[event delegation](https://www.geeksforgeeks.org/event-delegation-in-javascript/)
pattern.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const { on } = component("my-component");

on(".btn").click = ({ e }) => {
  console.log(".btn is clicked!");
};
```

Outside event handler. By assigning `on.outside.event`, you can handle the event
outside of the component dom.

```js
import { component } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";

const { on } = component("my-component");

on.outside.click = ({ e }) => {
  console.log("The outside of my-component has been clicked!");
};
```

# API reference

```ts
const { component, mount } from "https://deno.land/x/capsule@v0.6.0/dist.min.js";
```

## `component(name): ComponentResult`

This registers the component of the given name. This returns a `ComponentResult`
which has the following shape.

```ts
interface ComponentResult {
  on: EventRegistryProxy;
  is(name: string);
  sub(type: string);
  innerHTML(html: string);
}

interface EventRegistry {
  [key: string]: EventHandler | {};
  (selector: string): {
    [key: string]: EventHandler;
  };
  outside: {
    [key: string]: EventHandler;
  };
}
```

## `component().on[eventName] = EventHandler`

You can register event handler by assigning to `on.event`.

```ts
const { on } = component("my-component");

on.click = () => {
  alert("clicked");
};
```

## `component().on(selector)[eventName] = EventHandler`

You can register event handler by assigning to `on(selector).event`.

The actual event handler is attached to the component dom (the root of element
which this component mounts), but the handler is only triggered when the target
is inside the given `selector`.

```ts
const { on } = component("my-component");

on(".btn").click = () => {
  alert(".btn is clicked");
};
```

## `component().on.outside[eventName] = EventHandler`

You can register event handler for the outside of the component dom by assigning
to `on.outside.event`

```ts
const { on } = component("my-component");

on.outside.click = () => {
  console.log("outside of the component has been clicked!");
};
```

This is useful for implementing a tooltip which closes itself if the outside of
it is clicked.

## `component().is(name: string)`

`is(name)` sets the html class to the component dom at `mount` phase.

```ts
const { is } = component("my-component");

is("my-class-name");
```

## `component().innerHTML(html: string)`

`innerHTML(html)` sets the inner html to the component dom at `mount` phase.

```ts
const { innerHTML } = component("my-component");

innerHTML("<h1>Greetings!</h1><p>Hello from my-component</p>");
```

## `component().sub(type: string)`

`sub(type)` sets the html class of the form `sub:type` to the component at
`mount` phase. By adding `sub:type` class, the component can receive the event
from `pub(type)` calls.

```ts
{
  const { sub, on } = component("my-component");
  sub("my-event");
  on["my-event"] = () => {
    alert("Got my-event");
  };
}
{
  const { on } = component("another-component");
  on.click = ({ pub }) => {
    pub("my-event");
  };
}
```

## `EventHandler`

The event handler in `capsule` has the following signature. The first argument
is `EventHandlerContext`, not `Event`.

```ts
type EventHandler = (ctx: ComponentEventContext) => void;
```

## `ComponentEventContext`

```ts
interface ComponentEventContext {
  e: Event;
  el: Element;
  pub<T = unknown>(name: string, data: T): void;
  query(selector: string): Element | null;
  queryAll(selector: string): NodeListOf<Element> | null;
}
```

`e` is the native DOM Event. You can call APIs like `.preventDefault()` or
`.stopPropagation()` via this object.

`el` is the DOM Element, which the event handler is bound to, and the event is
dispatched on.

You can optionally attach data to the event. The attached data is available via
`.detail` property of `CustomEvent` object.

`pub(type)` dispatches the event to the remote elements which have `sub:type`
class. This should be used with `sub(type)` calls. For example:

```ts
{
  const { sub, on } = component("my-component");
  sub("my-event");
  on["my-event"] = () => {
    alert("Got my-event");
  };
}
{
  const { on } = component("another-component");
  on.click = ({ pub }) => {
    pub("my-event");
  };
}
```

This call dispatches `new CustomEvent("my-type")` to the elements which have
`sub:my-type` class, like `<div class="sub:my-type"></div>`. The event doesn't
bubbles up.

This method is for communicating with the remote elements which aren't in
parent-child relationship.

## `mount(name?: string, el?: Element)`

This function initializes the elements with the given configuration. `component`
call itself initializes the component of the given class name automatically when
document got ready, but if elements are added after the initial page load, you
need to call this method explicitly to initialize capsule's event handlers.

```js
// Initializes the all components in the entire page.
mount();

// Initializes only "my-component" components in the entire page.
// You can use this when you only added "my-component" component.
mount("my-compnent");

// Initializes the all components only in `myDom` element.
// You can use this when you only added something under `myDom`.
mount(undefined, myDom);

// Initializes only "my-component" components only in `myDom` element.
// You can use this when you only added "my-component" under `myDom`.
mount("my-component", myDom);
```

## `unmount(name: string, el: Element)`

This function unmounts the component of the given name from the element. This
removes the all event listeners of the component and also calls the
`__unmount__` hooks.

```js
const { on } = component("my-component");

on.__unmount__ = () => {
  console.log("unmounting!");
};

unmount("my-component", el);
```

Note: It's ok to just remove the mounted elements without calling `unmount`.
Such removals don't cause a problem in most cases, but if you use `outside`
handlers, you need to call unmount to prevent the leakage of the event handler
because outside handlers are bound to `document` object.

# How `capsule` works

This section describes how `capsule` works in a big picture.

Let's look at the below basic example.

```js
const { on } = component("my-component");

on.click = () => {
  console.log("clicked");
};
```

This code is roughly translated into jQuery like the below:

```js
$(document).read(() => {
  $(".my-component").each(function () {
    $this = $(this);

    if (isAlreadyInitialized($this)) {
      return;
    }

    $this.click(() => {
      console.log("clicked");
    });
  });
});
```

`capsule` can be seen as a syntax sugar for the above pattern (with a few more
utilities).

# Prior art

- [capsid](https://github.com/capsidjs/capsid)
  - `capsule` is heavily inspired by `capsid`

# Projects with similar concepts

- [Flight](https://flightjs.github.io/) by twitter
  - Not under active development
- [eddy.js](https://github.com/WebReflection/eddy)
  - Archived

# History

- 2022-01-13 v0.5.2 Change `el` typing. #2
- 2022-01-12 v0.5.1 Fix `__mount__` hook execution order
- 2022-01-12 v0.5.0 Add tests, setup CI.
- 2022-01-11 v0.4.0 Add outside handlers.
- 2022-01-11 v0.3.0 Add `unmount`.
- 2022-01-11 v0.2.0 Change delegation syntax.

# License

MIT