When will you use this?

Add routing when your app has more than one screen and URLs should be bookmarkable.

• Multi-page apps like dashboards use React Router — /settings, /profile, /orders.
• E-commerce sites route /product/123 to a product detail component.

Real-world: HDFC API client with interceptors

Banking SPA uses axios instance with base URL, JWT injection, and global 401 handler that redirects to login.

Production-style code

import axios from 'axios';

export const bankingApi = axios.create({
  baseURL: 'https://api.hdfc.example/v1',
  timeout: 15000
});

bankingApi.interceptors.request.use(config => {
  const token = sessionStorage.getItem('accessToken');
  if (token) config.headers.Authorization = `Bearer ${token}`;
  return config;
});

bankingApi.interceptors.response.use(
  res => res,
  err => {
    if (err.response?.status === 401) window.location.href = '/login';
    return Promise.reject(err);
  }
);

What happens in production: One configured client serves accounts, transfers, and cards — DRY auth and error handling across 40+ endpoints.

Lesson example (start here)

Copy this smaller example first. Once it works, compare it with the real-world code above.

import axios from 'axios';

const api = axios.create({ baseURL: '/api' });

api.interceptors.request.use(config => {
  const token = localStorage.getItem('token');
  if (token) config.headers.Authorization = `Bearer ${token}`;
  return config;
});

const { data } = await api.get('/users');

Line-by-line walkthrough

How it works (big picture)

• create sets base URL once.
• Interceptor runs before each request.
• await api.get throws if server returns error status.

Do this on your computer

1. npm install axios
2. Create api.js with axios.create.
3. Import api in components instead of raw fetch.
4. Read the real-world section and name which part of the app uses this topic.
5. Run the example locally and confirm the same behavior in the browser.
6. Change one value in the example (text, initial state, or URL) and predict what will happen before you save.

Experiments — try changing this

• Change text or labels in the example and save — watch the browser update.
• Break the code on purpose (remove a bracket), read the error message, then fix it.
• Open React DevTools (browser extension) while running Axios and inspect component props/state.

Remember

One shared axios instance per app. Interceptors for auth and errors. async/await with try/catch.

Common questions