Hot Module Replacement#

Hot Module Replacement (HMR) exchanges, adds, or removes modules while an application is running, without a full reload. This can significantly speed up development in a few ways:

• Retain application state which is lost during a full reload.
• Save valuable development time by only updating what's changed.
• Instantly update the browser when modifications are made to CSS / JS in the source code, which is almost comparable to changing styles directly in the browser's dev tools.

HMR Toggle#

Rsbuild has built-in support for HMR, which is enabled by default in development mode.

If you do not need to use HMR, you can set dev.hmr to false. This will disable HMR and react-refresh will, and Rsbuild will automatically fallback to dev.liveReload.

export default {
  dev: {
    hmr: false,
  },
};

If you need to disable both HMR and liveReload, you can set both dev.hmr and dev.liveReload to false. Then, no Web Socket requests will be made to the dev server on the page, and the page will not automatically refresh when files change.

export default {
  dev: {
    hmr: false,
    liveReload: false,
  },
};

Specify HMR URL#

By default, Rsbuild uses the host and port number of the current page to splice the WebSocket URL for HMR.

When the HMR connection fails, you can specify the WebSocket URL by customizing dev.client config.

export default {
  dev: {
    client: {
      host: 'localhost',
      protocol: 'ws',
    },
  },
};

File Watching#

By default, Rsbuild does not watching files in the .git/ and node_modules/ directories. When files in these directories changed, Rsbuild will not trigger a rebuild. This helps to reduce memory usage and improve build performance.

If you want to watch these directories, you can manually configure Rspack's watchOptions.ignored to override the default behavior.

For example, to watch the node_modules/ directory and ignore the .git/ directory, you can configure it as follows:

export default {
  tools: {
    rspack: {
      watchOptions: {
        ignored: /\.git/,
      },
    },
  },
};

FAQ#

Please refer to HMR FAQ.