Hooks in action: implementing a 1KB React router

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Hooks in Action: Implementing a 1KB Router in React Alexey Taktarov @mlfrg · molefrog.com

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Alexey Taktarov believes that design > engineering currently busy working on resume.io 4M+ resumes worldwide, distributed team !+" @mlfrg molefrog molefrog Twitter GitHub Instagram

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image source: http://inrussia.com/the-vyborg-library V I I P U R I L I B R A R Y — A L V A R A A L T O , 1 9 3 5

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source: http://inrussia.com/the-vyborg-library

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“the mission of an architect is to give life a more sensitive structure and to put the material world into harmony with human life” Alvar Aalto image source: http://inrussia.com/the-vyborg-library

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the function of building can be fulfilled by the combination of the fundamental elements: air, light, materials

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Let’s get back to React…

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React Hooks — the building blocks of an interface logic

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useState → useReducer allows to subscribe to primitive state value changes

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const [value, setValue] = useState(0); // custom hooks const [value, setValue] = useGlobalState(0); const [value, setValue] = useLocalStorageState(0); Hooks are composable: one interface, diﬀerent behaviour

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learn React Hooks by implementing a real open-source project: a tiny router for React What are we going to do today?

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Routing in React apps routing approaches have transformed along with the React ecosystem

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const routes = ( ); React Router v1.0.3: a DSL for describing routes

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v4: no outlets, no top-level configs in favour of a simple component:

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fewer constraints → more freedom

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Minimal Viable Router: implementing router’s core hooks useLocation and useRouter

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location.pathname router

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const [location, setLocation] = useLocation(); useLocation: the tiniest router ever

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const useLocation = () => { const [location, setLocation] = useState(location.pathname); // call `setLocation` whenever the pathname changes return [location, to => history.pushState(0, 0, to)]; }; if pathname changes → re-render

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mount — subscribe, unmount — unsubscribe const useLocation = () => { const [location, setLocation] = useState(location.pathname); // call `setLocation` whenever the pathname changes useEffect(() => { // subscribe to pushState/replaceState return () => { /* unsub */ } }, []); return [location, to => history.pushState(0, 0, to)]; };

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Hooks pro-tip #1: always specify useEﬀect dependencies! const useLocation = () => { const [location, setLocation] = useState(location.pathname); // call `setLocation` whenever the pathname changes useEffect(() => { // subscribe to pushState/replaceState return () => { /* unsub */ } }, []); return [location, to => history.pushState(0, 0, to)]; };

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useEﬀect a gate to subscriptions; a replacement for lifecycle-methods

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how do we subscribe to pushState/replaceState?

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how to subscribe to pushState/replaceState? monkey-patch these methods intercept link clicks → github.com/storeon/router → github.com/molefrog/wouter

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how do I test hooks? hooks are «special» functions, they can’t run outside of React reconciler

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import { renderHook, act } from "react-hooks-testing-library"; it("reacts to pushState / replaceState", () => { const { result, unmount } = renderHook(() => useLocation()); act(() => history.pushState(0, 0, "/foo")); expect(result.current[0]).toBe("/foo"); unmount(); }); testing hooks = testing components

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pattern-based routing?

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/users/:id/info /users/22/info => true, id: 22 pattern-based routing?

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useRoute("/users/:id") => [true, { id: 13 }]

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https://github.com/pillarjs/path-to-regexp path-to-regexp powers libraries like express and React Router

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Adding Components Route, Link and Switch

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useRoute is quite handy, but results in boilerplate const UserPage = () => { const [match, params] = useRoute("/users/:id") if (!match) return null; return `User id: ${params.id}`; }

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let’s design Route component

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import { createElement as h } from "react"; const Route = ({ path, component }) => { const [match, params] = useRoute(path); if (!match) return null; return h(component, { params: params }); }

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Adding a navigation About Us

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const Link = props => { const [_, navigate] = useLocation(); const handleClick = useCallback( event => { event.preventDefault(); navigate(href); }, [href, navigate] ); // render link }; hooks pro-tip #2: use useCallback for event handlers; this makes your code optimizitation-friendly

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useMemo → useCallback use it to describe computed values with proper caching

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How useEﬀect and useMemo process dependencies A B C D A A A A A B A B always stale, recomputed on every render undefined always fresh, computed once [] recomputed only when either x or y changes [x, y]

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// all of these should produce the same html // Contact Contact Contact Contact

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how do we add a prop to an element? if (isValidElement(children)) { return cloneElement(children, { href, onClick: handleClick }); }

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Switch Component Exclusive routing and default routes

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/users/all →

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/users/22 →

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/foo/bar →

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Children.forEach(children, element => { if (isValidElement(element)) { const [match] = matcher(element.props.path, location); /* render element in case of a match */ }); isValidElement ﬁlters out these things: “foo”, 122 etc. see Switch implementation from React Router

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Towards a 1KB router! Our bundle is 2.2KB already, let’s drop some things out path-to-regexp — 65%

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pathToRegexp what we need? case-sensitive, partial matching case insensitive, match the entire string nameless params /:foo/(.*) simple modifiers /:foo*, /:foo? и /:foo+ typed params /icon-:foo(\d+).png —

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https://github.com/molefrog/wouter/issues/1 2.2KB → 1.1KB

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Size Limit helps to keep your library in good shape https://github.com/ai/size-limit

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making the matcher backwards-compatible?

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you can always specify an original matcher through the optional top-level Router

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const Router = props => { const ref = useRef(null); // this little trick allows to avoid having unnecessary // calls to potentially expensive `buildRouter` method. const router = ref.current || (ref.current = buildRouter(props)); // provide router using context: }; should only create router once!

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useRef saves the value between re-renders; replaces this.*

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accessing router from any component?

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useContext a «portal» from the context

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const useRouter = () => { const providedRouter = useContext(RouterCtx); // either obtain the router from the outer context // (provided by the ` component) or create // a default one on demand. return useMemo( () => (providedRouter ? providedRouter : buildRouter()), [providedRouter] ); } useMemo allows to make the top-level Router optional

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const useRouter = () => { const providedRouter = useContext(RouterCtx); // either obtain the router from the outer context // (provided by the ` component) or create // a default one on demand. return useMemo( () => (providedRouter ? providedRouter : buildRouter()), [providedRouter] ); } we need a way to save a router somewhere «globally»

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// one of the coolest features of React Context: // when no value is provided, default object is used. const GlobalRefCtx = createContext({ current: null }) const useGlobalRef = () => useContext(GlobalRefCtx) Hooks pro-tip #3: a global Ref trick — one value shared between multiple components. No needed!

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we’ve got a nice extension point now! // useStaticLocation, useGlobalState, useLocalStorage, ... by customising a useLocation hook we can achieve some interesting effects: like hash-based routing, or persisted routing

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Supporting Preact conquering new markets

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import { useRoute } from "wouter/preact";

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copy sources into preact/ folder   on prepublishOnly NPM event ├── index.js ├── react-deps.js └── preact ├── index.js └── react-deps.js (* preact)

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// make sure the children prop is always an array // note: returns [[]] in case of an empty array! children = children && children.length ? children : [children]; children in Preact is always an array

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Conclusion what did we get?

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useState useEﬀect useMemo useRef useContext ?

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useImperativeHandle use it when you want to control your components in imperative way

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followed the lifecycle of an open-source library: from design to the launch

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Meet Wouter: github.com/molefrog/wouter

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! For all Wouters in the audience: no oﬀence!

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«form follows function» principle a top-down design

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Alexey Taktarov @mlfrg · molefrog.com Illustrations Font used Simacheva Katya instagram.com/simacheva.katya Zangezi Sans, Daria Petrova futurefonts.xyz/daria-petrova/zangezi-sans Project repo github.com/molefrog/wouter