choo

:steam_locomotive::train::train::train::train::train:

Fun functional programming

A 5kb framework for creating sturdy frontend applications

Handbook | Ecosystem | CLI | Contributing | Chat

_{The little framework that could. Built with ❤︎ by
Yoshua Wuyts and

contributors}

Table of Contents

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: [![built with choo v4](https://img.shields.io/badge/built%20with%20choo-v4-ffc3e4.svg?style=flat-square)](https://github.com/yoshuawuyts/choo) ```md [![built with choo v4](https://img.shields.io/badge/built%20with%20choo-v4-ffc3e4.svg?style=flat-square)](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.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.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. ## FAQ ### Why is it called choo? Because I thought it sounded cute. All these programs talk about being _"performant"_, _"rigid"_, _"robust"_ - I like programming to be light, fun and non-scary. `choo` embraces that. Also imagine telling some business people you chose to rewrite something critical to the company using `choo`. :steam_locomotive::train::train::train: ### Why is it a framework, and not a library? I love small libraries that do one thing well, but when working in a team, having an undocumented combination of packages often isn't great. `choo()` is a small set of packages that work well together, wrapped in an an architectural pattern. This means you get all the benefits of small packages, but get to be productive right from the start without needing to plough through layers of boilerplate. ### Is it called choo, choo.js or...? It's called "choo", though we're fine if you call it "choo-choo" or "chugga-chugga-choo-choo" too. The only time "choo.js" is tolerated is if / when you shimmy like you're a locomotive. ### How does choo compare to X? Ah, so this is where I get to rant. `choo` (_chugga-chugga-chugga-choo-choo!_) was built because other options didn't quite cut it for me, so instead of presenting some faux-objective chart with skewed benchmarks and checklists I'll give you my opinions directly. Ready? Here goes: - __react:__ despite being at the root of a giant paradigm shift for frontend (thank you forever!), `react` is kind of big (`155kb` was it?). They also like classes a lot, and enforce a _lot_ of abstractions. It also encourages the use of `JSX` and `babel` which break _JavaScript, The Language™_. And all that without making clear how code should flow, which is crucial in a team setting. I don't like complicated things and in my view `react` is one of them. `react` is not for me. - __mithril:__ never used it, never will. I didn't like the API, but if you like it maybe it's worth a shot - the API seems small enough. I wouldn't know how pleasant it is past face value. - __preact:__ a pretty cool idea; seems to fix most of what is wrong with `react`. However it doesn't fix the large dependencies `react` seems to use (e.g. `react-router` and friends) and doesn't help at all with architecture. If `react` is your jam, and you will not budge, sitting at `3kb` this is probably a welcome gift. - __angular:__ definitely not for me. I like small things with a clear mental model; `angular` doesn't tick any box in my book of nice things. - __angular2:__ I'm not sure what's exactly changed, but I know the addition of `TypeScript` and `RxJS` definitely hasn't made things simpler. Last I checked it was `~200kb` in size before including some monstrous extra deps. I guess `angular` and I will just never get along. - __mercury:__ ah, `mercury` is an interesting one. It seemed like a brilliant idea until I started using it - the abstractions felt heavy, and it took team members a long time to pick up. In the end I think using `mercury` helped shaped `choo` greatly, despite not working out for me. - __deku:__ `deku` is fun. I even contributed a bit in the early days. It could probably best be described as "a functional version of `react`". The dependence on `JSX` isn't great, but give it a shot if you think it looks neat. - __cycle:__ `cycle`'s pretty good - unlike most frameworks it lays out a clear architecture which helps with reasoning about it. That said, it's built on `virtual-dom` and `xstream` which are a bit heavy for my taste. `choo` works pretty well for FRP style programming, but something like [inu] might be an interesting alternative. - __vue:__ like `cycle`, `vue` is pretty good. But it also uses tech that provides framework lock in, and additionally doesn't have a clean enough architecture. I appreciate what it does, but don't think it's the answer. ### Why can't send() be called on the server? In Node, `reducers`, `effects` and `subscriptions` are disabled for performance reasons, so if `send()` was called to trigger an action it wouldn't work. Try finding where in the DOM tree `send()` is called, and disable it when called from within Node. ### Which packages was choo built on? - __views:__ [`yo-yo`][yo-yo], [`bel`][bel] - __models:__ [`barracks`](https://github.com/yoshuawuyts/barracks), [`xtend`](https://github.com/raynos/xtend) - __routes:__ [`sheet-router`][sheet-router] - __http:__ [`xhr`](https://github.com/Raynos/xhr) ### Does choo use a virtual-dom? `choo` uses [morphdom][morphdom], which diffs real DOM nodes instead of virtual nodes. It turns out that [browsers are actually ridiculously good at dealing with DOM nodes][morphdom-bench], and it has the added benefit of working with _any_ library that produces valid DOM nodes. So to put a long answer short: we're using something even better. ### How can I optimize choo? `choo` really shines when coupled with `browserify` transforms. They can do things like reduce file size, prune dependencies and clean up boilerplate code. Consider running some of the following: - [unassertify](https://github.com/twada/unassertify) - remove `assert()` statements which reduces file size. Use as a `--global` transform - [es2020](https://github.com/yoshuawuyts/es2020) - backport `const`, `arrow functions` and `template strings` to older browsers. Should be run as a `--global` transform - [yo-yoify](https://github.com/shama/yo-yoify) - replace the internal `hyperx` dependency with `document.createElement` calls; greatly speeds up performance too - [uglifyify](https://github.com/hughsk/uglifyify) - minify your code using UglifyJS2. Use as a `--global` transform - [bulkify](https://www.npmjs.com/package/bulkify) - transform inline [bulk-require](https://www.npmjs.com/package/bulk-require) calls into statically resolvable require maps - [envify](https://github.com/hughsk/envify) - replace `process.env` values with plain strings ### Choo + Internet Explorer & Safari Out of the box `choo` only supports runtimes which support: * `const` * `arrow functions` (e.g. `() => {}`) * `template strings` This does not include Safari 9 or any version of IE. If support for these platforms is required you will have to provide some sort of transform that makes this functionality available in older browsers. The test suite uses [es2020](https://github.com/yoshuawuyts/es2020) as a global transform, but anything else which might satisfy this requirement is fair game. Generally for production builds you'll want to run: ```sh $ NODE_ENV=production browserify \ -t envify \ -g yo-yoify \ -g unassertify \ -g es2020 \ -g uglifyify \ | uglifyjs ``` ## Hey, doesn't this look a lot like Elm? Yup, it's greatly inspired by the `elm` architecture. But contrary to `elm`, `choo` doesn't introduce a completely new language to build web applications. ### Is it production ready? Sure. ## Browser Test Status

## Installation ```sh $ npm install choo ``` ## See Also - [choo-handbook](https://github.com/yoshuawuyts/choo-handbook) - the little `choo` guide - [awesome-choo](https://github.com/YerkoPalma/awesome-choo) - Awesome things related with choo framework - [kaktus](https://github.com/kaktus/kaktus) - A new minimalistic web browser - [budo](https://github.com/mattdesl/budo) - quick prototyping tool for `browserify` - [stack.gl](http://stack.gl/) - open software ecosystem for WebGL - [yo-yo](https://github.com/maxogden/yo-yo) - tiny library for modular UI - [bel](https://github.com/shama/bel) - composable DOM elements using template strings - [tachyons](https://github.com/tachyons-css/tachyons) - functional CSS for humans - [sheetify](https://github.com/stackcss/sheetify) - modular CSS bundler for `browserify` - [pull-stream](https://github.com/pull-stream/pull-stream) - minimal streams - [es2020](https://github.com/yoshuawuyts/es2020) - because in hindsight we don't need most of ES6 ## Support Creating a quality framework takes a lot of time. Unlike others frameworks, Choo is completely independently funded. We fight for our users. This does mean however that we also have to spend time working contracts to pay the bills. This is where you can help: by chipping in you can ensure more time is spent improving Choo rather than dealing with distractions. ### Sponsors Become a sponsor and help ensure the development of independent quality software. You can help us keep the lights on, bellies full and work days sharp and focused on improving the state of the web. [Become a sponsor](https://opencollective.com/choo#sponsor)

### Backers Become a backer, and buy us a coffee (or perhaps lunch?) every month or so. [Become a backer](https://opencollective.com/choo#backer)

## License [MIT](https://tldrlegal.com/license/mit-license) [bankai]: https://github.com/yoshuawuyts/bankai [bel]: https://github.com/shama/bel [browserify]: https://github.com/substack/node-browserify [budo]: https://github.com/mattdesl/budo [es2020]: https://github.com/yoshuawuyts/es2020 [handbook]: https://github.com/yoshuawuyts/choo-handbook [hyperx]: https://github.com/substack/hyperx [inu]: https://github.com/ahdinosaur/inu [morphdom-bench]: https://github.com/patrick-steele-idem/morphdom#benchmarks [morphdom]: https://github.com/patrick-steele-idem/morphdom [sheet-router]: https://github.com/yoshuawuyts/sheet-router [yo-yo]: https://github.com/maxogden/yo-yo