What is react-hot-loader?

React Hot Loader was a tool for developers building web apps with React, a popular JavaScript library for creating user interfaces. Normally, when you change code during development, the browser refreshes and you lose whatever you were doing, such as the text you typed into a form or which tab you had open. This tool let you edit your components and see the result update instantly in the browser without a full refresh, preserving that in-progress state. The project is now officially deprecated. The README recommends removing it and switching to React Fast Refresh, which is a newer solution built more directly into the tools most developers already use. React Native has supported Fast Refresh since version 0.61, webpack has a plugin for it, and create-react-app and Next.js both include it by default in recent versions. For projects still using it, setup involved three steps: adding a Babel plugin to your project configuration, wrapping your top-level app component with a helper called hot, and making sure the library loaded before React itself. Babel is a tool that transforms JavaScript code, and this plugin was what allowed the hot-reload magic to work. There was also an optional patched version of react-dom available for projects that needed deeper hook support. The tool was safe to include in production builds. It detected the environment and disabled itself automatically, leaving almost no extra size in the final bundle. That meant developers did not need separate configuration for development versus production builds. There were a few known limits. The tool preserved existing component state and did not re-run lifecycle events when code changed, which was intentional. Changes to a component's constructor were also not always reliably applied to components that were already mounted on the page. The full README is longer than what was shown.