webpack/hot/only-dev-server.js

if(module.hot) {
	var lastData;
	var upToDate = function upToDate() {
		return lastData.indexOf(__webpack_hash__) >= 0;
	};
	var check = function check() {
		module.hot.check(function(err, updatedModules) {
			if(err) {
				if(module.hot.status() in {abort:1,fail:1}) {
					console.warn("[HMR] Cannot check for update. Need to do a full reload!");
				} else {
					console.warn("[HMR] Update check failed: " + err);
				}
				return;
			}

			if(!updatedModules) {
				console.warn("[HMR] Cannot find update. Need to do a full reload!");
				console.warn("[HMR] (Probably because of restarting the webpack-dev-server)")
				return;
			}

			module.hot.apply({
				ignoreUnaccepted: true
			}, function(err, renewedModules) {
				if(err) {
					if(module.hot.status() in {abort:1,fail:1}) {
						console.warn("[HMR] Cannot apply update (Need to do a full reload!): " + err);
					} else {
						console.warn("[HMR] Update failed: " + err);
					}
					return;
				}

				if(!upToDate()) {
					check();
				}

				var unacceptedModules = updatedModules.filter(function(moduleId) {
					return renewedModules.indexOf(moduleId) < 0;
				});

				if(unacceptedModules.length > 0) {
					console.warn("[HMR] The following modules couldn't be hot updated: (They would need a full reload!)");
					unacceptedModules.forEach(function(moduleId) {
						console.warn("[HMR]  - " + moduleId);
					});
				}

				if(!renewedModules || renewedModules.length === 0) {
					console.log("[HMR] Nothing hot updated.");
				} else {
					console.log("[HMR] Updated modules:");
					renewedModules.forEach(function(moduleId) {
						console.log("[HMR]  - " + moduleId);
					});
				}
				if(upToDate()) {
					console.log("[HMR] App is up to date.");
				}


			});
		});
	};
	var addEventListener = window.addEventListener ? function(eventName, listener) {
		window.addEventListener(eventName, listener, false);
	} : function (eventName, listener) {
		window.attachEvent('on' + eventName, listener);
	};
	addEventListener("message", function(event) {
		if(typeof event.data === "string" && event.data.indexOf("webpackHotUpdate") === 0) {
			lastData = event.data;
			if(!upToDate() && module.hot.status() === "idle") {
				console.log("[HMR] Checking for updates on the server...");
				check();
			}
		}
	});
	console.log("[HMR] Waiting for update signal from WDS...");
} else {
	throw new Error("[HMR] Hot Module Replacement is disabled.");
}