Hot Module Replacement (HMR) is a feature of Webpack bundler that updates your JavaScript components without refreshing the entire page. This makes it very useful during development as it speeds up development process and improves developer experience by preserving the state of the application even after file changes.
In ReactJS, HMR works with the help of react-hot-loader – a babel plugin that uses HMR API to make your React components hot-reloadable.
Here are the steps of how HMR works in React:
1. When a file is edited and saved, webpack will detect changes.
2. Module that has changed and the modules that depend on it are replaced.
3. Webpack will notify React Hot Loader about the update.
4. React Hot Loader will use React’s component updating mechanism to only update the components that have changed, without causing a full re-render of your application.
5. The state of your updated component will remain the same where it should.
Note: Developers need to configure webpack and Babel to use Hot Module Replacement with React. React Hot Loader will take care of the rest.
```
// How you use hot module replacement in React:
if (module.hot) {
module.hot.accept(‘./app’, function() {
console.log(‘Accepting the updated module!’);
render(App)
})
}
```
Remember that HMR is great for development, but it should be properly disabled for your production environment.
