// Modified copy of https://github.com/webpack/webpack/blob/v1.11.0/hot/only-dev-server.js
// (Added window.instrumentCodeGroupAsyncTopLevel)

/*
  MIT License http://www.opensource.org/licenses/mit-license.php
  Author Tobias Koppers @sokra
*/
/*globals window __webpack_hash__ */
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!");
          console.warn("[HMR] " + err.stack || err.message);
        } else {
          console.warn("[HMR] Update check failed: " + err.stack || err.message);
        }
        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;
      }

      window.instrumentCodeGroupAsyncTopLevel('Webpack HMR', 'Webpack Hot Module Replacement', function() {
        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!");
              console.warn("[HMR] " + err.stack || err.message);
            } else {
              console.warn("[HMR] Update failed: " + err.stack || err.message);
            }
            return;
          }

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

          require("webpack/hot/log-apply-result")(updatedModules, renewedModules);

          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.");
}

Add modified version of a Webpack hot loading file
Add modified version of a Webpack hot loading file

Which makes use of grouping calls, so you don’t get a crazy amount of
top-level calls when re-rendering React components.