javascript 32 lines · 6 steps

Lazy-loaded routes in React

Split each page into its own bundle and load it on demand, with a spinner and an error net around the swap.

Explained by highlit
React Intermediate code-splitting lazy-loading routing error-boundaries suspense
1import { lazy, Suspense } from "react";
2import { Routes, Route, NavLink } from "react-router-dom";
3import ErrorBoundary from "./components/ErrorBoundary";
4import Spinner from "./components/Spinner";
5 
6const Dashboard = lazy(() => import("./pages/Dashboard"));
7const Reports = lazy(() => import("./pages/Reports"));
8const Settings = lazy(() => import("./pages/Settings"));
9 
10export default function AppRoutes() {
11 return (
12 <div className="app-shell">
13 <nav className="sidebar">
14 <NavLink to="/" end>Dashboard</NavLink>
15 <NavLink to="/reports">Reports</NavLink>
16 <NavLink to="/settings">Settings</NavLink>
17 </nav>
18 
19 <main className="content">
20 <ErrorBoundary fallback={<p>Failed to load this section.</p>}>
21 <Suspense fallback={<Spinner label="Loading…" />}>
22 <Routes>
23 <Route path="/" element={<Dashboard />} />
24 <Route path="/reports" element={<Reports />} />
25 <Route path="/settings" element={<Settings />} />
26 </Routes>
27 </Suspense>
28 </ErrorBoundary>
29 </main>
30 </div>
31 );
32}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Wrapping dynamic imports in lazy() lets each route ship as a separate chunk fetched only when visited.
  2. 2Suspense supplies a loading fallback for any lazy child while its bundle downloads.
  3. 3An ErrorBoundary outside Suspense catches chunk-load failures so a bad network doesn't blank the whole app.

Related explainers

javascript 
function evaluate(expression) {
  const tokens = tokenize(expression);
  let pos = 0;
 

Building a recursive descent calculator

parsing recursion operator-precedence
Intermediate 8 steps
javascript 
import { useState, useEffect, useCallback, useRef } from 'react';
 
const cache = new Map();
const inflight = new Map();

Building a stale-while-revalidate hook in React

caching request-deduplication custom-hooks
Advanced 10 steps
javascript 
import { useEffect, useRef, useState } from 'react';
 
export function useDelayedFlag(active, delay = 300) {
  const [visible, setVisible] = useState(false);

Delaying a loading spinner with a React hook

custom-hooks debouncing cleanup
Intermediate 8 steps
javascript 
const SWIPE_THRESHOLD = 80;
const MAX_TRANSLATE = 120;
 
export function attachSwipeToDismiss(element, onDismiss) {

Building a swipe-to-dismiss gesture in JS

touch-events gesture-detection dom-manipulation
Intermediate 10 steps
javascript 
const { pool } = require('./db');
 
function withTransaction() {
  return async (req, res, next) => {

A per-request transaction middleware in Express

middleware database-transactions connection-pooling
Advanced 7 steps
javascript 
function collapseConsecutiveLogs(lines, { keyFn = (l) => l.message } = {}) {
  const groups = [];
 
  for (const line of lines) {

Collapsing consecutive log lines in JavaScript

grouping run-length-encoding data-transformation
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

Lazy-loaded routes in React — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code