Make it Declarative with React @koba04 / JSConf JP 2019 

Toru Kobayashi @koba04 Twitter / GitHub Web Developer 2007 ～ Cybozu →Frontend Expert Team SmartHR →Frontend Advisor 

ReactVoice ReactVoice. .render render( ( < <> > < > こんにちは こんにちは < > < > I I work work as as a frontend developer a frontend developer for for Cybozu and Cybozu and I I work work as as a frontend advisor a frontend advisor for for SmartHR SmartHR. . < > < >My Twitter and GitHub accounts are @koba04 My Twitter and GitHub accounts are @koba04< > < > I I'm also one 'm also one of of the organizers the organizers of of React React. .js meetup js meetup in in Tokyo and Tokyo and a contributor a contributor of of React React. . < > < >I I've been working 've been working with with React React for for 5 5years years. .< > < >, , { {} } ) ); ; 

Agenda Benefits of Declarative Programming for UI Custom renderer of React Live Demo! 

Declarative Programming for UI 

Declarative Programming https://en.wikipedia.org/wiki/Declarative_programming In computer science, declarative programming is a programming paradigm—a style of building the structure and elements of computer programs—that expresses the logic of a computation without describing its control flow. Many languages that apply this style attempt to minimize or eliminate side effects by describing what the program must accomplish in terms of the problem domain, rather than describe how to accomplish it as a sequence of the programming language primitives 

Why Declarative? What Not How How -> Compiler Abstraction layer Optimization in the underlying layer Primitive as domain 

The logic of a computation without describing its control flow 

DOM manipulation is based on imperative operations 

Imperative const const view view = = document document. .querySelector querySelector( ('.view' '.view') ); ; const const addButton addButton = = document document. .querySelector querySelector( ('.add-button' '.add-button') ); ; // You have to implement how to update the view // You have to implement how to update the view addButton addButton. .addEventListener addEventListener( ('click' 'click', , ( () ) => => { { view view. .appendChild appendChild( (child child) ) } }) ); ; 

Declarative const const view view = = document document. .querySelector querySelector( ('.view' '.view') ); ; const const addButton addButton = = document document. .querySelector querySelector( ('.add-button' '.add-button') ); ; const const state state = = [ [] ]; ; addButton addButton. .addEventListener addEventListener( ('click' 'click', , ( () ) => => { { // update the state impleratively // update the state impleratively state state. .push push( (child child) ); ; // describe the view declaratively based on the state // describe the view declaratively based on the state render render( (state state) ); ; } }) ); ; // describing what the view should display // describing what the view should display const const render render = = state state => => { { view view. .innerHTML innerHTML = = state state. .map map( (s s => => ` ` ${ ${s s} } ` `) ). .join join( ('' '') ); ; } } Describing what to update the view 

= View(State) 

React updates views efficiently let let count count = = 1 1; ; ReactDOM ReactDOM. .render render( ( <

ReactDOM Renderer 

Describing what the program must accomplish in terms of the problem domain 

Abstract your application components DOM is an implementation detail React Component is a primitive of your domain. 

Build own domain layers with React const const view view = = document document. .querySelector querySelector( ('.view' '.view') ); ; // describing what the view should display // describing what the view should display const const App App = = ( () ) => => { { const const [ [items items, , setItems setItems] ] = = useState useState( ([ [] ]) ); ; return return ( ( < > < >title title< > < > { {items items. .map map( (item item => => < >) )} } < > < => setItems setItems( (items items. .concat concat( (item item) )) )} } / /> > < > ) ); ; } } ReactDOM ReactDOM. .render render( (< >, , view view) ); ; 

DOM as a Second-class Citizen Sebastian Markbåge - DOM as a Second-cl Sebastian Markbåge - DOM as a Second-cl… … 後で見る 後で見る 共有 共有 Sebastian Markbåge / React Europe 2015 

React Custom Renderer 

Renderers 

Ink import import React React from from 'react' 'react'; ; import import { {render render, , Box Box, , Color Color} } from from 'ink' 'ink'; ; render render( ( < > < >Hello world Hello world! !< > < > ) ); ; 

ReactKonva ReactKonva ReactKonva. .render render( ( < > < > < > < > < > < >, , el el ) ); ; 

ReactThreeFiber import import React React, , { { useRef useRef } } from from 'react' 'react' import import ReactDOM ReactDOM from from 'react-dom' 'react-dom' import import { { Canvas Canvas, , useFrame useFrame } } from from 'react-three-fiber' 'react-three-fiber' const const Cube Cube = = ( () ) => => { { const const ref ref = = useRef useRef( () ) useFrame useFrame( (( () ) => => ( (ref ref. .current current. .rotation rotation. .x x = = ref ref. .current current. .rotation rotation. .y y += += 0.01 0.01) )) ) return return ( ( < > < > < > < > ) ) } } ReactDOM ReactDOM. .render render( (< >< >< >, , el el) ); ; 

ReactAST import import React React from from 'react' 'react'; ; import import { { renderAst renderAst, , Code Code, , ClassDeclaration ClassDeclaration, , FunctionDeclaration FunctionDeclaration } } from from 'react-ast' 'react-ast'; ; const const ast ast = = renderAst renderAst( ( < > < >const const hello hello = = 'world' 'world'< > < > < >return return 'bar' 'bar'< > < > < > ) ); ; console console. .log log( (ast ast) ); ; 

Building a Custom React DOM Renderer https://github.com/jquense/react-dom-lite https://conf.reactjs.org/event.html?sophiebits 

Architecture of React https://speakerdeck.com/koba04/algorithms-in-react 

react-reconciler npm install react-reconciler npm install react-reconciler packages/react-reconciler 

How to use import import Reconciler Reconciler from from "react-reconciler" "react-reconciler"; ; const const renderer renderer = = Reconciler Reconciler( (hostconfig hostconfig) ); ; export export const const YourReact YourReact = = { { render render( ( element element: : React React. .ReactNode ReactNode, , rootContainer rootContainer: : RootContainer RootContainer, , callback callback = = ( () ) => => { {} } ) ) { { if if ( (! !rootContainer rootContainer. .container container) ) { { rootContainer rootContainer. .container container = = { {} } rootContainer rootContainer. .container container. .fiberRoot fiberRoot = = renderer renderer. .createContainer createContainer( ( container container, , false false, , false false ) ); ; } } renderer renderer. .updateContainer updateContainer( (element element, , container container. .fiberRoot fiberRoot, , null null, , callback callback) ); ; } } } } 

HostConfig Interface #1 Mutation(optional) getPublicInstance, getRootHostContext, getChildHostContext, prepareForCommit, resetAfterCommit, createInstance, appendInitialChild, finalizeInitialChildren, prepareUpdate, shouldSetTextContent, shouldDeprioritizeSubtree, createTextInstance scheduleDeferredCallback, cancelDeferredCallback, setTimeout, clearTimeout, noTimeout, now, isPrimaryRenderer supportsMutation, supportsPersistence, supportsHydration appendChild, appendChildToContainer, commitTextUpdate, commitMount, commitUpdate, insertBefore, insertInContainerBefore, removeChild, removeChildFromContainer, resetTextContent 

HostConfig Interface #2 Persistence(optional) Hydration(optional) from @types/react-reconciler cloneInstance, createContainerChildSet, appendChildToContainerChildSet, finalizeContainerChildren, replaceContainerChildren canHydrateInstance, canHydrateTextInstance, getNextHydratableSibling, getFirstHydratableChild, hydrateInstance hydrateTextInstance,didNotMatchHydratedContainerTextInstance, didNotMatchHydratedTextInstance, didNotHydrateContainerInstance, didNotHydrateInstance,didNotFindHydratableContainerInstance, didNotFindHydratableContainerTextInstance, didNotFindHydratableInstance, didNotFindHydratableTextInstance 

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HostConfig of renderers ReactDOM packages/react-dom/src/client/ReactDOMHostConfig.js ReactNative packages/react-native-renderer/src/ReactNativeHostConfig.js packages/react-native-renderer/src/ReactFabricHostConfig.js ReactTestRenderer packages/react-test-renderer/src/ReactTestHostConfig.js Ink vadimdemedes/ink/blob/master/src/reconciler.js ReactKonva konvajs/react-konva/blob/master/src/ReactKonvaHostConfig.js 

HostConfig? Side effects for a Host environment Define instances Define the mode for a renderer Hydration logic (if you need) 

Side effects for a Host environment ReactDOM ReactDOM. .render render( ( <

> <
• >a a< > <
• >b b< > <
• >c c< > < >, , container container ) ); ; ReactDOM ReactDOM. .render render( ( <
  > <
  • >b b< > <
  • >a a< > <
  • >c c< > < >, , container container ) ) // React update the DOM like the following // React update the DOM like the following // li.insertBefore(b, a); // li.insertBefore(b, a); 

Side effects for a Host environment export export function function insertBefore insertBefore( ( parentInstance parentInstance: : Instance Instance, , child child: : Instance Instance | | TextInstance TextInstance, , beforeChild beforeChild: : Instance Instance | | TextInstance TextInstance ) ): : void void { { // we have to remove a current instance at first // we have to remove a current instance at first const const index index = = parentInstance parentInstance. .children children. .indexOf indexOf( (child child) ); ; if if ( (index index !== !== - -1 1) ) { { parentInstance parentInstance. .children children. .splice splice( (index index, , 1 1) ); ; } } // And then, we insert the instance into a new index // And then, we insert the instance into a new index const const beforeIndex beforeIndex = = parentInstance parentInstance. .children children. .indexOf indexOf( (beforeChild beforeChild) ); ; parentInstance parentInstance. .children children. .splice splice( (beforeIndex beforeIndex, , 0 0, , child child) ); ; } } 

Others appendChild, appendInitialChild, appendChildToContainer commitTextUpdate, commitMount, commitUpdate insertBefore, insertInContainerBefore removeChild, removeChildFromContainer, resetTextContent 

createInstance, createTextInstance export export function function createInstance createInstance( ( type type: : Type Type, , props props: : Props Props, , rootContainerInstance rootContainerInstance: : Container Container, , hostContext hostContext: : HostContext HostContext, , internalInstanceHandle internalInstanceHandle: : OpaqueHandle OpaqueHandle ) ): : Instance Instance { { return return createYourHostInstance createYourHostInstance( (type type, , props props) ); ; } } export export function function createTextInstance createTextInstance( ( text text: : string string, , rootContainerInstance rootContainerInstance: : Container Container, , hostContext hostContext: : HostContext HostContext, , internalInstanceHandle internalInstanceHandle: : OpaqueHandle OpaqueHandle ) ): : TextInstance TextInstance { { return return createYourTextInstacne createYourTextInstacne( (text text) ); ; } } 

getPublicInstance export export function function getPublicInstance getPublicInstance( ( instance instance: : Instance Instance ) ): : PublicInstance PublicInstance { { return return convertToPublicInstance convertToPublicInstance( (instance instance) ); ; // react-dom // react-dom // return instance; // return instance; } } 

Define the mode for a renderer export export const const isPrimaryRenderer isPrimaryRenderer = = true true; ; export export const const supportsMutation supportsMutation = = true true; ; export export const const supportsPersistence supportsPersistence = = false false; ; export export const const supportsHydration supportsHydration = = false false; ; 

Type Definition for custom host config declare namespace declare namespace JSX JSX { { interface interface IntrinsicElements IntrinsicElements { { text text: : { { color color: : string string; ; children children? ?: : React React. .ReactNode ReactNode; ; } }; ; } } } } https://www.typescriptlang.org/docs/handbook/jsx.html#intrinsic-elements 

Live Coding 

Thank you!!! speakerdeck.com/koba04/ github.com/koba04/jsconf-jp-presentation