React Routing をマスターする: アプリケーションをナビゲートするための完全ガイド

1. Introduction to React Router

React Router is a library for handling routing in React applications. It allows your app to navigate between different components and views without a full-page reload, making the user experience seamless.

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2. Basic Setup

Start by installing react-router-dom:

npm install react-router-dom

Set up basic routing using BrowserRouter, Routes, and Route:

import React from 'react';
import { BrowserRouter as Router, Routes, Route, Link } from 'react-router-dom';

const Home = () => <h2 id="Home">Home</h2>;
const About = () => <h2 id="About">About</h2>;

const App = () => {
  return (
    <router>
      <nav>
        <link to="/">Home
        <link to="/about">About
      </nav>

      <routes>
        <route path="/" element="{<Home"></route>} />
        <route path="/about" element="{<About"></route>} />
      </routes>
    </router>
  );
};

export default App;

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3. Nested Routing

For more complex apps, you can nest routes. Here’s how to set up nested routes in a parent component:

import React from 'react';
import { BrowserRouter as Router, Routes, Route, Link } from 'react-router-dom';

const Dashboard = () => <h2 id="Dashboard-Home">Dashboard Home</h2>;
const Profile = () => <h2 id="Your-Profile">Your Profile</h2>;

const DashboardLayout = () => {
  return (
    <div>
      <nav>
        <link to="/dashboard">Home
        <link to="/dashboard/profile">Profile
      </nav>
      <routes>
        <route path="/" element="{<Dashboard"></route>} />
        <route path="profile" element="{<Profile"></route>} />
      </routes>
    </div>
  );
};

const App = () => {
  return (
    <router>
      <routes>
        <route path="/dashboard/*" element="{<DashboardLayout"></route>} />
      </routes>
    </router>
  );
};

export default App;

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4. Dynamic Routing

Dynamic routing allows you to pass parameters in the URL. Here’s how to define and access a dynamic route:

import { useParams } from 'react-router-dom';

const User = () => {
  const { id } = useParams();
  return <h2 id="User-ID-id">User ID: {id}</h2>;
};

const App = () => {
  return (
    <router>
      <nav>
        <link to="/user/1">User 1
        <link to="/user/2">User 2
      </nav>

      <routes>
        <route path="/user/:id" element="{<User"></route>} />
      </routes>
    </router>
  );
};

export default App;

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5. Protected Routes

To implement protected routes, you can create a custom PrivateRoute component:

import { Navigate, Outlet } from 'react-router-dom';

const useAuth = () => {
  const user = { loggedIn: true }; // Replace with actual auth logic
  return user && user.loggedIn;
};

const PrivateRoute = () => {
  const isAuth = useAuth();
  return isAuth ? <outlet></outlet> : <navigate to="/login"></navigate>;
};

const App = () => {
  return (
    <router>
      <routes>
        <route path="/login" element="{<Login"></route>} />
        <route path="/dashboard" element="{<PrivateRoute"></route>}>
          <route path="" element="{<Dashboard"></route>} />
        
      </routes>
    </router>
  );
};

export default App;

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6. Programmatic Navigation

Sometimes, you may want to navigate programmatically, like after a form submission. Use the useNavigate hook in React Router v6:

import { useNavigate } from 'react-router-dom';

const Login = () => {
  const navigate = useNavigate();

  const handleLogin = () => {
    // Login logic here...
    navigate('/dashboard');
  };

  return (
    <div>
      <h2 id="Login">Login</h2>
      <button onclick="{handleLogin}">Login</button>
    </div>
  );
};

export default Login;

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7. 404 Pages

Handle 404 (Not Found) errors by creating a catch-all route:

const NotFound = () => <h2 id="Page-Not-Found">404 - Page Not Found</h2>;

const App = () => {
  return (
    <router>
      <routes>
        <route path="/" element="{<Home"></route>} />
        <route path="/about" element="{<About"></route>} />
        <route path="*" element="{<NotFound"></route>} />
      </routes>
    </router>
  );
};

export default App;

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8. Performance Considerations

For large applications, lazy loading routes can improve performance. Here’s how to implement lazy loading with React.lazy() and Suspense:

import React, { Suspense, lazy } from 'react';
import { BrowserRouter as Router, Routes, Route } from 'react-router-dom';

const Home = lazy(() => import('./Home'));
const About = lazy(() => import('./About'));

const App = () => {
  return (
    <router>
      <suspense fallback="{<div">Loading...}>
        <routes>
          <route path="/" element="{<Home"></route>} />
          <route path="/about" element="{<About"></route>} />
        </routes>
      </suspense>
    </router>
  );
};

export default App;

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