webpack/webpack · error · Error

[HMR] Hot Module Replacement is disabled.

Error message

[HMR] Hot Module Replacement is disabled.

What it means

hot/dev-server.js is the universal HMR client runtime shipped into the bundle. Its entire body is guarded by `if (module.hot)`; the else branch throws because the client can do nothing useful without the HMR runtime. `module.hot` is injected only when HotModuleReplacementPlugin is active and the build targets HMR.

Source

Thrown at hot/dev-server.js:91

		if (!upToDate() && module.hot.status() === "idle") {
			log("info", "[HMR] Checking for updates on the server...");
			check();
		}
	};

	if (typeof EventTarget !== "undefined" && hotEmitter instanceof EventTarget) {
		hotEmitter.addEventListener(
			"webpackHotUpdate",
			/** @type {EventListener} */
			(handler)
		);
	} else {
		hotEmitter.on("webpackHotUpdate", handler);
	}

	log("info", "[HMR] Waiting for update signal from WDS...");
} else {
	throw new Error("[HMR] Hot Module Replacement is disabled.");
}

View on GitHub (pinned to 318421ea8a)

Solutions

1. Keep `devServer.hot` unset or true (the default in development) so the HMR runtime is injected.
2. Ensure `mode: 'development'` (or manually apply HotModuleReplacementPlugin).
3. If using webpack-dev-server, let it inject its own client — do not also add hot/dev-server.js to entry manually.
4. For production builds, exclude the HMR client entirely (no hot/* references).

Example fix

// webpack.config.js — before
devServer: { hot: false },  // client throws: Hot Module Replacement is disabled.

// after
devServer: { hot: true },   // or simply omit `hot`

// webpack.config.js — make HMR availability explicit
module.exports = {
  mode: 'development',
  devServer: { hot: true },
  plugins: [new webpack.HotModuleReplacementPlugin()],
};

// runtime guard for code that conditionally uses the HMR client
function isHotRuntime() {
  return typeof module !== 'undefined' && module.hot !== null && module.hot !== undefined;
}

When it happens

Trigger: The dev-server HMR client chunk is included in the entry/output but `module.hot` is undefined at runtime — i.e. HotModuleReplacementPlugin was not applied, devServer.hot was set to false, or a production build accidentally pulled in the HMR client.

Common situations: Setting `devServer: { hot: false }` while the client entry still references hot/dev-server; building for production with mode that strips the HMR runtime; a custom setup that injects the WDS client into a non-HMR build; mixing webpack-dev-middleware without the HMR plugin.

Related errors

• [HMR] Hot Module Replacement is disabled.
• [HMR] Hot Module Replacement is disabled.
• [HMR] Hot Module Replacement is disabled.
• check() is only allowed in idle status
• apply() is only allowed in ready status (state: " + currentS

AI-assisted analysis of webpack/webpack@318421ea8a (2026-08-03). Data as JSON: /data/errors/501e47920f4de663.json. Report an issue: GitHub.