## Features
- __minimal size:__ weighing `5kb`, `choo` is a tiny little framework
- __single state:__ immutable single state helps reason about changes
- __small api:__ with only 6 methods, there's not a lot to learn
- __minimal tooling:__ built for the cutting edge `browserify` compiler
- __transparent side effects:__ using `effects` and `subscriptions` brings
clarity to IO
- __omakase:__ composed out of a balanced selection of open source packages
- __isomorphic:__ renders seamlessly in both Node and browsers
- __very cute:__ choo choo!
## Demos
- :truck: [Input example](http://requirebin.com/?gist=229bceda0334cf30e3044d5f5c600960)
([repo](examples/title/))
- :water_buffalo: [HTTP effects example](https://fork-fang.hyperdev.space/)
([repo](https://hyperdev.com/#!/project/fork-fang))
- :mailbox: [Mailbox routing](examples/mailbox/)
- :ok_hand: [TodoMVC](http://shuheikagawa.com/todomvc-choo/)
([repo](https://github.com/shuhei/todomvc-choo))
- :fire: [Choo-firebase](https://github.com/fyrkant/choo-firebase)
- :seedling: [Grow](https://grow.static.land/)
([repo](https://github.com/sethvincent/grow))
- :newspaper: [Hacker News Reader](https://hackernews-choo.surge.sh/) ([repo](https://github.com/kvnneff/hackernews-choo))
- :earth_africa: [Thing Translator](https://oxism.com/thing-translator/) ([repo](https://github.com/dmotz/thing-translator))
_note: If you've built something cool using `choo` or are using it in
production, we'd love to hear from you!_
## Example
Let's create an input box that changes the content of a textbox in real time.
[Click here to see the app running](http://requirebin.com/?gist=229bceda0334cf30e3044d5f5c600960).
```js
var html = require('choo/html')
var choo = require('choo')
var app = choo()
app.model({
state: { title: 'Not quite set yet' },
reducers: {
update: function (state, data) {
return { title: data }
}
}
})
function mainView (state, prev, send) {
return html`
Title: ${state.title}
`
function update (e) {
send('update', e.target.value)
}
}
app.router(['/', mainView])
var tree = app.start()
document.body.appendChild(tree)
```
To run it, save it as `client.js` and run with [bankai][bankai]. `bankai` is
convenient but any [browserify][browserify] based tool should do:
```sh
# run and reload on port 8080
$ bankai client.js -p 8080 --open
# compile to static files in `./dist/`
$ bankai build index.js dist/
# deploy to github pages using `tschaub/gh-pages`
$ gh-pages -d dist/
```
## Philosophy
We believe programming should be fun and light, not stern and stressful. It's
cool to be cute; using serious words without explaining them doesn't make for
better results - if anything it scares people off. We don't want to be scary,
we want to be nice and fun, and then _casually_ be the best choice around.
_Real casually._
We believe frameworks should be disposable, and components recyclable. We don't
like the current state of web development where walled gardens jealously
compete with one another. We want you to be free, not shackled to a damp
dungeon wall. By making the DOM the lowest common denominator, switching from
one framework to another becomes frictionless. Components should run anywhere
that has a DOM, regardless of the framework. `choo` is modest in its design; we
don't believe it will be top of the class forever, so we've made it as easy to
toss out as it is to pick up.
We don't believe that bigger is better. Big APIs, big dependencies, large file
sizes - we see them as omens of impending userland complexity. We want
everyone on a team, no matter the size, to fully understand how an application
is laid out. And once an application is built, we want it to be small,
performant and easy to reason about. All of which makes for easy to debug code,
better results and super smiley faces.
## Concepts
`choo` cleanly structures internal data flow, so that all pieces of logic can
be combined into a nice, cohesive machine. Roughly speaking there are two parts
to `choo`: the views and the models. Models take care of state and logic, and
views are responsible for displaying the interface and responding to user
interactions.
All of `choo`'s state is contained in a single object and whenever it changes
the views receive a new version of the state which they can use to safely
render a complete new representation of the DOM. The DOM is efficiently updated
using DOM diffing/patching.
The logic in choo exist in three different kinds of actions, each with their
own role: `effects`, `subscriptions` and `reducers`.
- __Effects__ makes an asynchronous operation and calls another action when
it's done.
- __Subscriptions__ (called once when the DOM loads) listens for external input
like keyboard or WebSocket events and then calls another action.
- __Reducers__ receives the current state and returns an updated version of the
state which is then sent to the views.
```txt
┌─────────────────┐
│ Subscriptions ─┤ User ───┐
└─ Effects ◀─────┤ ▼
┌─ Reducers ◀─────┴─────────── DOM ◀┐
│ │
└▶ Router ─────State ───▶ Views ────┘
```
### Models
`models` are objects that contain initial `state`, `subscriptions`, `effects`
and `reducers`. They're generally grouped around a theme (or domain, if you
like). To provide some sturdiness to your `models`, they can either be
namespaced or not. Namespacing means that only state within the model can be
accessed. Models can still trigger actions on other models, though it's
recommended to keep that to a minimum.
So say we have a `todos` namespace, an `add` reducer and a `todos` model.
Outside the model they're called by `send('todos:add')` and
`state.todos.items`. Inside the namespaced model they're called by
`send('todos:add')` and `state.items`. An example namespaced model:
```js
var app = choo()
app.model({
namespace: 'todos',
state: { items: [] },
reducers: {
add: function (state, data) {
return { items: state.items.concat(data.payload) }
}
}
})
```
In most cases using namespaces is beneficial, as having clear boundaries makes
it easier to follow logic. But sometimes you need to call `actions` that
operate over multiple domains (such as a "logout" `action`), or have a
`subscription` that might trigger multiple `reducers` (such as a `websocket`
that calls a different `action` based on the incoming data).
In these cases you probably want to have a `model` that doesn't use namespaces,
and has access to the full application state. Try and keep the logic in these
`models` to a minimum, and declare as few `reducers` as possible. That way the
bulk of your logic will be safely shielded, with only a few points touching every
part of your application.
### Effects
`effects` are similar to `reducers` except instead of modifying the state they
cause side `effects` by interacting servers, databases, DOM APIs, etc. Often
they'll call a reducer when they're done to update the state. For instance, you
may have an effect called getUsers that fetches a list of users from a server
API using AJAX. Assuming the AJAX request completes successfully, the effect
can pass off the list of users to a reducer called receiveUsers which simply
updates the state with that list, separating the concerns of interacting with
an API from updating the application's state.
This is an example `effect` that is called once when the application loads and
calls the `'todos:add'` `reducer` when it receives data from the server:
```js
var choo = require('choo')
var http = require('xhr')
var app = choo()
app.model({
namespace: 'todos',
state: { values: [] },
reducers: {
add: function (state, data) {
return { todos: data }
}
},
effects: {
addAndSave: function (state, data, send, done) {
var opts = { body: data.payload, json: true }
http.post('/todo', opts, function (err, res, body) {
if (err) return done(err)
data.payload.id = body.id
send('todos:add', data, function (err, value) {
if (err) return done(err)
done(null, value)
})
})
}
},
subscriptions: {
'called-once-when-the-app-loads': function (send, done) {
send('todos:addAndSave', done)
}
}
})
```
### Subscriptions
Subscriptions are a way of receiving data from a source. For example when
listening for events from a server using `SSE` or `Websockets` for a
chat app, or when catching keyboard input for a videogame.
An example subscription that logs `"dog?"` every second:
```js
var choo = require('choo')
var app = choo()
app.model({
namespace: 'app',
effects: {
print: function (state, data) {
console.log(data.payload)
}
},
subscriptions: {
callDog: function (send, done) {
setInterval(function () {
var data = { payload: 'dog?', myOtherValue: 1000 }
send('app:print', data, function (err) {
if (err) return done(err)
})
}, 1000)
}
}
})
```
If a `subscription` runs into an error, it can call `done(err)` to signal the
error to the error hook.
### Router
The `router` manages which `views` are rendered at any given time. It also
supports rendering a default `view` if no routes match.
```js
var app = choo()
app.router({ default: '/404' }, [
[ '/', require('./views/empty') ],
[ '/404', require('./views/error') ],
[ '/:mailbox', require('./views/mailbox'), [
[ '/:message', require('./views/email') ]
]]
])
```
Routes on the `router` are passed in as a nested array. This means that the
entry point of the application also becomes a site map, making it easier to
figure out how views relate to each other.
Under the hood `choo` uses [sheet-router]. Internally the
currently rendered route is kept in `state.location`. To access the route
`:params` you can use `state.location.params`. If you want to modify
the location programmatically the `reducer` for the location can be called
using `send('location:set', href)`. This will not work
from within namespaced `models`, and usage should preferably be kept to a
minimum. Changing views all over the place tends to lead to messiness.
### Views
Views are pure functions that return a DOM tree for the router to render.
They’re passed the current state, and any time the state changes they’re run
again with the new state.
Views are also passed the `send` function, which they can use to dispatch
actions that can update the state. For example, the DOM tree can have an
`onclick` handler that dispatches an `add` action.
```js
function view (state, prev, send) {
return html`
Total todos: ${state.todos.length}
`
function addTodo (e) {
send('add', { title: 'demo' })
}
}
```
In this example, when the `Add` button is clicked, the view will dispatch an
`add` action that the model’s `add` reducer will receive. [As seen
above](#models), the reducer will add an item to the state’s `todos` array. The
state change will cause this view to be run again with the new state, and the
resulting DOM tree will be used to [efficiently patch the
DOM](#does-choo-use-a-virtual-dom).
### Plugins
Sometimes it's necessary to change the way `choo` itself works. For example to
report whenever an action is triggered, handle errors globally or perist state
somewhere. This is done through something called `plugins`. Plugins are objects
that contain `hook` and `wrap` functions and are passed to `app.use()`:
```js
var log = require('choo-log')
var choo = require('choo')
var app = choo()
app.use(log())
var tree = app.start()
document.body.appendChild(tree)
```
Generally people using `choo` shouldn't be too worried about the specifics of
`plugins`, as the internal API is (unfortunately by necessity) quite complex.
After all they're the most powerful way to modify a `choo` application.
__:warning: Warning :warning:: plugins should only be used as a last resort.
It creates peer dependencies which makes upgrading versions and switching
frameworks a lot harder. Please exhaust all other options before using
plugins.__
If you want to learn more about creating your own `plugins`, and which `hooks`
and `wrappers` are available, head on over to [app.use()](#appusehooks).
## Badges
Using `choo` in a project? Show off which version you've used using a badge:
[](https://github.com/yoshuawuyts/choo)
```md
[](https://github.com/yoshuawuyts/choo)
```
## API
This section provides documentation on how each function in `choo` works. It's
intended to be a technical reference. If you're interested in learning choo for
the first time, consider reading through the [handbook] or
[concepts](#concepts) first :sparkles:
### app = choo(opts)
Initialize a new `choo` app. Takes an optional object of handlers that is
passed to [app.use()](#appusehooks).
### app.model(obj)
Create a new model. Models modify data and perform IO. Takes the following
arguments:
- __namespace:__ namespace the model so that it cannot access any properties
and handlers in other models
- __state:__ initial values of `state` inside the model
- __reducers:__ synchronous operations that modify state. Triggered by
`actions`. Signature of `(state, data)`.
- __effects:__ asynchronous operations that don't modify state directly.
Triggered by `actions`, can call `actions`. Signature of `(state, data,
send, done)`
- __subscriptions:__ asynchronous read-only operations that don't modify state
directly. Can call `actions`. Signature of `(send, done)`.
#### send(actionName, data?[,callback])
Send a new action to the models with optional data attached. Namespaced models
can be accessed by prefixing the name with the namespace separated with a `:`,
e.g. `namespace:name`.
When sending data from inside a `model` it expects exactly three arguments: the name of the action you're calling, the data you want to send, and finally a callback to handle errors through the global `onError()` hook. So if you want to send two values, you'd have to either send an array or object containing them.
#### done(err?, res?)
When an `effect` or `subscription` is done executing, or encounters an error,
it should call the final `done(err, res)` callback. If an `effect` was called
by another `effect` it will call the callback of the caller. When an error
propegates all the way to the top, the `onError` handler will be called,
registered in `choo(handlers)`. If no callback is registered, errors will
`throw`.
### app.router(defaultRoute?, (route) => [routes])
Creates a new router. Takes a function that exposes a single `route` function,
and that expects a tree of `routes` to be returned. See [sheet-router] for full
documentation. Registered views have a signature of `(state, prev, send)`,
where `state` is the current `state`, `prev` is the last state,
`state.location.params` is URI partials and `send()` can be called to trigger
actions. If `defaultRoute` is passed in, that will be called if no paths match.
If no `defaultRoute` is specified it will throw instead.
### app.use(hooks)
Register an object of hooks on the application. This is useful to extend the
way `choo` works, adding custom behavior and listeners. Generally returning
objects of `hooks` is done by returning them from functions (which we call
`plugins` throughout the documentation).
There are several `hooks` and `wrappers` that are picked up by `choo`:
- __onError(err, state, createSend):__ called when an `effect` or
`subscription` emit an error. If no handler is passed, the default handler
will `throw` on each error.
- __onAction(state, data, name, caller, createSend):__ called when an
`action` is fired.
- __onStateChange(state, data, prev, caller, createSend):__ called after a
reducer changes the `state`.
- __wrapSubscriptions(fn):__ wraps a `subscription` to add custom behavior
- __wrapReducers(fn):__ wraps a `reducer` to add custom behavior
- __wrapEffects(fn):__ wraps an `effect` to add custom behavior
- __wrapInitialState(fn):__ mutate the complete initial `state` to add custom
behavior - useful to mutate the state before starting up
__:warning: Warning :warning:: plugins should only be used as a last resort.
It creates peer dependencies which makes upgrading versions and switching
frameworks a lot harder. Please exhaust all other options before using
plugins.__
`createSend()` is a special function that allows the creation of a new named
`send()` function. The first argument should be a string which is the name, the
second argument is a boolean `callOnError` which can be set to `true` to call
the `onError` hook istead of a provided callback. It then returns a
`send(actionName, data?)` function.
Hooks should be used with care, as they're the most powerful interface into
the state. For application level code it's generally recommended to delegate to
actions inside models using the `send()` call, and only shape the actions
inside the hooks.
### html = app.toString(route, state?)
Render the application to a string of HTML. Useful for rendering on the server.
First argument is a path that's passed to the router. Second argument is an
optional state object. When calling `.toString()` instead of `.start()`, all
calls to `send()` are disabled, and `subscriptions`, `effects` and `reducers`
aren't loaded.
### tree = app.start(opts)
Start the application. Returns a tree of DOM nodes that can be mounted using
`document.body.appendChild()`. Opts can contain the following values:
- __opts.history:__ default: `true`. Enable a `subscription` to the browser
history API. e.g. updates the internal `location.href` state whenever the
browsers "forward" and "backward" buttons are pressed.
- __opts.href:__ default: `true`. Handle all relative `` clicks and update internal `state.location`
accordingly.
- __opts.hash:__ default: `false`. Enable a `subscription` to the hash change
event, updating the internal `state.location` state whenever the URL hash
changes (eg `localhost/#posts/123`). Enabling this option automatically
disables `opts.history` and `opts.href`.
### view = require('choo/html')\`html\`
Tagged template string HTML builder. Built on top of [yo-yo], [bel], and
[hyperx]. To register a view on the `router` it should be wrapped in a function
with the signature of `(state, prev, send)` where `state` is the current
`state`, `prev` is the last state, `state.location.params` is URI partials and
`send()` can be called to trigger actions.
To create listeners for events, create interpolated attributes on elements.
```js
var html = require('choo/html')
html`
`
function log (e) {
console.log(e)
}
```
Example listeners include: `onclick`, `onsubmit`, `oninput`, `onkeydown`,
`onkeyup`. A full list can be found [at the yo-yo
repo](https://github.com/maxogden/yo-yo/blob/master/update-events.js). When
creating listeners always remember to call `e.preventDefault()` and
`e.stopPropagation()` on the event so it doesn't bubble up and do stuff like
refreshing the full page or the like.
To trigger lifecycle events on any part of a view, set the `onload=${(el) =>
{}}` and `onunload=${(el) => {}}` attributes. These parameters are useful when
creating self-contained widgets that take care of their own state and lifecycle
(e.g. a maps widget) or to trigger animations. Most elements shouldn't have a
need for these hooks though.
### mount('selector', html)
Use `choo/mount` to mount a tree of DOMNodes at a given selector. This is
especially useful to mount a `` tag on the document body after rendering
from the server. It makes sure all `
