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mercury

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A truly modular frontend framework

To understand what I mean by truly modular just read the source

Examples

Hello world

var document = require('global/document');
var hg = require('mercury');
var h = require('mercury').h;

function App() {
    // define application state.
    var state = hg.struct({
        value: hg.value(0),
        handles: hg.value(null)
    });

    // define handles that react to events.
    state.handles.set(hg.handles({
        clicks: incrementCounter
    }, state));

    return state;
}

// declare view rendering.
App.render = function render(state) {
    return h('div.counter', [
        'The state ', h('code', 'clickCount'),
        ' has value: ' + state.value + '.', h('input.button', {
            type: 'button',
            value: 'Click me!',
            'ev-click': hg.event(state.handles.clicks)
        })
    ]);
};

function incrementCounter(state) {
    state.value.set(state.value() + 1);
}

hg.app(document.body, App(), App.render);

Basic Examples

Intermediate Examples

Unidirectional examples

The following examples demonstrate how you can mix & match mercury with other frameworks. This is possible because mercury is fundamentally modular.

Disclaimer: The following are neither "good" nor "bad" ideas. Your milage may vary on using these ideas

Motivation

Mercury vs React

mercury is similar to react, however it's larger in scope, it is better compared against om or quiescent

  • mercury leverages virtual-dom which uses an immutable vdom structure
  • mercury comes with observ-struct which uses immutable data for your state atom
  • mercury is truly modular, you can trivially swap out subsets of it for other modules
  • mercury source code itself is maintainable, the modules it uses are all small, well tested and well documented. you should not be afraid to use mercury in production as it's easy to maintain & fix.
  • mercury encourages zero dom manipulation in your application code. As far as your application is concerned elements do not exist. This means you don't need to reference DOM elements when rendering or when handling events
  • mercury is compact, it's 11kb min.gzip.js, that's smaller than backbone.
  • mercury strongly encourages FRP techniques and discourages local mutable state.
  • mercury is highly performant, it's faster then React / Om / ember+htmlbars in multiple benchmarks TodoMVC benchmark
    animation benchmark TodoMVC benchmark source
  • mercury comes with FP features like time-travel / easy undo out of the box.
  • mercury is lean, it's an weekend's read at 2.5kloc. (virtual-dom is 1.1kloc, an evening's read.) compared to react which is almost 20kloc (a month's read)

Modules

mercury is a small glue layer that composes a set of modules that solves a subset of the frontend problem.

If mercury is not ideal for your needs, you should check out the individual modules and see if you can re-use something.

Alternatively if the default set of modules in mercury doesn't work for you, you can just require other modules. It's possible to for example, swap out vtree with react or swap out observ-struct with backbone

Input, State, Render and Output

There are three pieces to mercury, Input (Controller), State (Model) and Render (View).

In a normal mercury app you define your top level Input which is a finite list of events.

You then define your top level state "atom". Generally you want a large fat state object for your entire application. We then wire all the events in Input up to some updating logic, i.e. every time an event occurs in Input we do some logic and then update the State.

Finally we define our Rendering logic as a single function that takes the entire state of our application and returns a virtual DOM representation of our UI. Every time the state changes we just call render and then update the DOM.

You may also need Output for your application, if we want to have some other side effect other then updating the UI, like sending a HTTP POST or writing to a websocket or persisting to indexedDB. Then we generally listen to changes in the state and have our side effect. Note that Render is just a specific subset of the Output of your application.

Rendering modules (The view layer)

For the view layer mercury uses a set of modules that come together and make it easy to work with a Virtual DOM.

In mercury the view is just a function that takes your application state and returns a virtual DOM representation. This makes writing your view really easy, you just write it top to bottom.

mercury then uses the following modules to make it really performant to use the virtual DOM to update the real DOM.

vtree is the module that contains the data structures for the virtual DOM. These are the primitive objects and values that the rendering functions in a mercury app will return.

vtree also contains the diffing algorithm used in mercury. Mercury uses a diffing algorithm on a virtual DOM to compute a minimal set of VPatch records that it can apply to the DOM.

vdom is the module that contains the create and patch algorithm for turning the vtree data structures into real DOM objects.

vdom/create-element is used to turn a virtual DOM into a real DOM. this is used for the initial rendering of your app.

vdom/patch is used to apply a series of VPatch records to a real DOM element.

You can also use vdom and min-document together on the server to generate HTML strings. min-document is a minimal fake DOM for use on the server, you can pass vdom any document you want. In this case min-document contains the logic to convert its fake DOM into a HTML string.

virtual-hyperscript is a module that makes it easier to create VTree nodes. It basically exports a h() function that creates a DSL similar to jade (just more brackets ;)).

virtual-hyperscript allows you to write your views in an expressive manner.

vdom-thunk is a module that increases the performance of building applications with a virtual DOM system. One of the important parts of using a virtual DOM and functional programming in general is to make extensive use of caching.

You can use vdom-thunk to effectively memoize a function that returns a virtual DOM node. This means if you call it twice with the same arguments it will not re-evaluate the function.

This basically means you only have to render that which has changed instead of rendering the entire virtual tree of your application.

It should be noted that vdom-thunk assumes arguments are immutable and thus does an O(1) === check to see whether the arguments has changed. This will only work if your state is immutable. Thankfully, observ-struct is immutable

main-loop is another optimization module for a virtual DOM system. Normally you would re-create the virtual tree every time your state changes. This is not optimum, with main-loop you will only update your virtual tree at most once per request animation frame.

main-loop basically gives you batching of your virtual DOM changes, which means if you change your model multiple times it will be rendered once asynchronously on the next request animation frame.

State modules (The model layer)

In mercury we use immutable data structure primitives to represent our model. Using immutable data structures allows you to use the vdom-thunk optimization.

mercury uses an observable state representation so that you can be notified of any changes.

Generally applications built with mercury will have a single top level state "atom". i.e. there is one large state object for your application and child components do not have local or hidden state. However we can directly embed the state of a child component in our top level state "atom" to achieve composition.

observ is the data structure used for observable data. It allows you to create a value for which you can listen for changes.

observ also comes with higher order functions like observ/computed that can be used to create new dependent observables. Generally these computed observables cannot be directly mutated but instead change when they data they rely on changes.

observ is basically an implementation of the Signal type that is normally used in FRP.

observ-struct is an observable that contains an object with a fixed number of keys. Generally the key-value pairs in observ-struct are themselves observables. You can change the value of any key in an observ-struct and the top level object will also change to be a new object with that key changed.

observ-struct uses shallow extension to ensure that every time the struct changes you get a fresh immutable object.

observ-array is an observable that contains an array of observables. It's generally recommended that this a heterogeneous array. You can change the value of any item in the array and the top level array will also change to be a new array.

observ-array uses shallow extension to ensure that every time the array changes (an item changes or an item is added or removed) you get a fresh immutable array.

observ-array has the benefit of being able to add or remove items from the array, where as observ-struct has a fixed number of keys and you cannot add more keys to an observ-struct

Input modules (The controller layer)

In mercury we model all the inputs to our application explicitly. We define an input object that contains a bunch of geval Event instances.

Somewhere else in our application we listen to the Input and run some logic and update our state when an event happens.

geval is our data structure for Events. it gives us a way of listening to events and a way of publishing them.

Most of the time you will either create a computed Event that emits events based on some raw source, like winddow scroll events or a websocket. Or you can create a mutable Event which you pass to the UI renderer so it can emit events for dynamically created UI components.

geval is basically an implementation of the Event type that is normally used in FRP.

dom-delegator is an event delegator that allows you to seperate your event listeners from your event emitters. It sets up global event listeners and allow you to embed event handlers on your virtual DOM elements without having to manage adding or removing actual event listeners.

value-event allows you to create event handlers that you can embed in a virtual DOM. These event handlers work with both the native DOM and dom-delegator.

value-event contains a set of higher order functions that allows you to write to a value to a geval Event when some user interaction occurs.

Using the higher order functions defined in value-event (change, submit, etc. ) allows you to not have to write any DOM event handling code in your application. value-event takes care of all the reading from the DOM.

Documentation

FAQ

See the FAQ document

API

WIP. In lieu of documentation please see examples :(

Installation

npm install mercury

Development

If you want to develop on mercury you can clone the code

git clone [email protected]:Raynos/mercury
cd mercury
npm install
npm test

npm run tasks

  • npm test runs the tests
  • npm run jshint will run jshint on the code
  • npm run disc will open discify (if globally installed)
  • npm run build will build the html assets for gh-pages
  • npm run examples will start a HTTP server that shows examples
  • npm run dist will create a distributed version of mercury

Inspirations

A lot of the philosophy and design of mercury is inspired by the following:

  • react for documenting and explaining the concept of a virtual DOM and its diffing algorithm
  • om for explaining the concept and benefits of immutable state and time travel.
  • elm for explaining the concept of FRP and having a reference implementation of FRP in JavaScript. I wrote a pre-cursor to mercury that was literally a re-implementation of elm in javascript (graphics)
  • reflex for demonstrating the techniques used to implement dynamic inputs.

Contributors

  • Raynos
  • Matt-Esch
  • neonstalwart
  • parshap
  • nrw

MIT Licenced

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