Lazy loaded React router routes loading anyway

Question

I've been trying to lazy load routes in React using React.lazy and Suspense. But some components are loading regardless of the current route, exactly: Feed, Profile and Settings.

Notice I don't actually want to lazy load Components like MenuAppBar and SnackAlert but if I import them normally and remove their Suspense, code-splitting straight doesn't even work and everything loads and the whole app is just a single chunk.

This is my network tab when on the homepage.

import {createMuiTheme, MuiThemeProvider} from "@material-ui/core";
import {yellow} from "@material-ui/core/colors";
import CssBaseline from "@material-ui/core/CssBaseline";
import axios from "axios";
import React, {lazy, Suspense, useEffect, useState} from "react";
import {BrowserRouter as Router, Route, Switch} from "react-router-dom";
import "./css/feed.css";
import "./css/style.css";

const Feed = lazy(() => import("./routes/Feed"));
const Profile = lazy(() => import("./routes/Profile"));
const Home = lazy(() => import("./routes/Home"));
const Settings = lazy(() => import("./routes/Settings"));
const NotFound = lazy(() => import("./routes/NotFound"));
const MenuAppBar = lazy(() => import("./components/MenuAppBar"));
const SnackAlert = lazy(() => import("./components/SnackAlert"));

const App: React.FC = () => {
    const [isLogged, setIsLogged] = useState(localStorage.getItem("token") ? true : false);

    const [user, setUser] = useState<User>(
        isLogged ? JSON.parse(localStorage.getItem("userInfo") as string) : {admin: false}
    );
    const [openError, setOpenError] = useState<boolean>(false);
    const [errorMsg, setErrorMsg] = useState<string>("");
    const [severity, setSeverity] = useState<Severity>(undefined);
    const [pwa, setPwa] = useState<any>(null);
    const [showBtn, setShowBtn] = useState<boolean>(false);
    const [isLight, setIsLight] = useState<boolean>(
        (JSON.parse(localStorage.getItem("theme") as string) as boolean) ? true : false
    );

    const theme: customTheme = {
        darkTheme: {
            palette: {
                type: "dark",
                primary: {
                    main: yellow[600]
                }
            }
        },
        lightTheme: {
            palette: {
                type: "light",
                primary: {
                    main: yellow[700]
                }
            }
        }
    };

    window.addEventListener("beforeinstallprompt", (event) => {
        event.preventDefault();
        setPwa(event);
        setShowBtn(true);
    });

    window.addEventListener("appinstalled", (e) => {
        setShowBtn(false);
        setErrorMsg("App installed!");
        setSeverity("success");
        setOpenError(true);
    });

    const handleClick = () => {
        if (/iPhone|iPad|iPod/i.test(navigator.userAgent)) {
            setErrorMsg(`Please, open the share menu and select "Add to Home Screen"`);
            setSeverity("info");
            setOpenError(true);
        } else {
            if (pwa) {
                pwa.prompt();
                pwa.userChoice.then((choiceResult: {outcome: "accepted" | "refused"}) => {
                    if (choiceResult.outcome === "accepted") {
                        setErrorMsg("App downloading in the background..");
                        setSeverity("info");
                        setOpenError(true);
                    }
                    setPwa(null);
                });
            }
        }
    };

    useEffect(() => {
        const token: string | null = localStorage.getItem("token");
        let userInfo: User = JSON.parse(localStorage.getItem("userInfo") as string);
        if (userInfo && token && !userInfo.admin) {
            setUser(userInfo);
            setIsLogged(true);
        }
        if (isLogged) {
            axios
                .get("/api/auth/user", {
                    headers: {
                        "x-auth-token": `${token}`
                    }
                })
                .then((res) => {
                    if (!userInfo || !token) {
                        setUser(res.data as User);
                    }
                    localStorage.setItem(`userInfo`, JSON.stringify(res.data as User));
                    setIsLogged(true);
                })
                .catch((err) => {
                    if (err) {
                        setIsLogged(false);
                    }
                });
        } else {
            localStorage.removeItem("token");
            localStorage.removeItem("userInfo");
        }
    }, [isLogged]);

    return (
        <MuiThemeProvider theme={isLight ? createMuiTheme(theme.lightTheme) : createMuiTheme(theme.darkTheme)}>
            <CssBaseline />
            <Router>
                <Suspense fallback={<div></div>}>
                    <Route
                        path="/"
                        render={() => (
                            <>
                                <MenuAppBar
                                    isLogged={isLogged}
                                    setIsLogged={setIsLogged}
                                    user={user}
                                    setUser={setUser}
                                    isLight={isLight}
                                    setIsLight={setIsLight}
                                />
                                <SnackAlert severity={severity} errorMsg={errorMsg} setOpenError={setOpenError} openError={openError} />
                            </>
                        )}
                    />
                </Suspense>
                <Suspense fallback={<div></div>}>
                    <Switch>
                        <Route exact path="/" render={() => <Home />} />

                        <Route exact path="/profile/:id" render={() => <Profile />} />

                        <Route exact path="/feed" render={() => <Feed isLogged={isLogged} user={user} />} />

                        <Route
                            exact
                            path="/settings"
                            render={() => (
                                <Settings isLight={isLight} setIsLight={setIsLight} handleClick={handleClick} showBtn={showBtn} />
                            )}
                        />
                        <Route render={() => <NotFound />} />
                    </Switch>
                </Suspense>
            </Router>
        </MuiThemeProvider>
    );
};

export default App;

Drew Reese Drew Reese · Accepted Answer · 2020-02-16T22:46:20

You are wrapping your entire Switch in a single Suspense, so all components will be lazily loaded at the same time. You probably only want each to be fetched/loaded when the specific route is rendered the first time.

<Switch>
  <Route
    exact
    path="/"
    render={props => (
      <Suspense fallback={<div>Loading...<div>}>
        <Home {...props} />
      </Suspense>
    )}
  />
  <Route
    exact
    path="/profile/:id"
    render={props => (
      <Suspense fallback={<div>Loading...<div>}>
        <Profile {...props} />
      </Suspense>
    )}
  />
  <Route
    exact
    path="/feed"
    render={() => (
      <Suspense fallback={<div>Loading...<div>}>
        <Feed isLogged={isLogged} user={user} {...props} />
      </Suspense>
    )}
  />
  <Route
    exact
    path="/settings"
    render={() => (
      <Suspense fallback={<div>Loading...<div>}>
        <Settings isLight={isLight} setIsLight={setIsLight} handleClick={handleClick} showBtn={showBtn} {...props} />
      </Suspense>
    )}
  />
  <Route
    render={() => <NotFound />}
  />
</Switch>

There is a lot of repetition here, so it is practical to factor out the suspense into a HOC.

const withSuspense = WrappedComponent => (
  <Suspense fallback={<div>Loading...<div>}>
    <WrappedComponent {...props} />
  </Suspense>
);

You can either decorate each perspective default export, i.e.

export default withSuspense(Home);

App.js

...
<Switch>
  <Route exact path="/" render={props => <Home {...props} />} />

or decorate them in your App

const HomeWithSuspense = withSuspense(Home);

...

<Switch>
  <Route
    exact
    path="/"
    render={props => <HomeWithSuspense {...props} />}
  />
  ...
</Switch>

Lazy loaded React router routes loading anyway

4 Answers