$ ng --version

   _           _         ____ _   ___
  / \  _ __  __ _ _  _| | __ _ _ __   / ___| |  |_ _|
  / △ \ | '_ \ / _` | | | | |/ _` | '__|  | |  | |  | |
 / ___ \| | | | (_| | |_| | | (_| | |   | |___| |___ | |
 /_/  \_\_| |_|\__, |\__,_|_|\__,_|_|    \____|_____|___|
        |___/


Angular CLI: 6.0.8
Node: 8.11.1
OS: win32 x64
Angular: 6.1.3
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

Package              Version
-----------------------------------------------------------
@angular-devkit/architect     0.6.8
@angular-devkit/build-angular   0.6.8
@angular-devkit/build-optimizer  0.6.8
@angular-devkit/core       0.6.8
@angular-devkit/schematics    0.6.8
@angular/cli           6.0.8
@ngtools/webpack         6.0.8
@schematics/angular        0.6.8
@schematics/update        0.6.8
rxjs               6.2.2
typescript            2.7.2
webpack              4.8.3

npm install --save-dev @angularclass/hmr --registry https://registry.npm.taobao.org

export const environment = {
 production: false,
 hmr: true
};

"compilerOptions": {
 ...
 "types": ["node"]
}

import { NgModuleRef, ApplicationRef } from "@angular/core";
import { createNewHosts } from "@angularclass/hmr";

export const hmrBootstrap = (
 module: any,
 bootstrap: () => Promise<NgModuleRef<any
) => {
 let ngModule: NgModuleRef<any>;
 module.hot.accept();
 bootstrap().then(mod => (ngModule = mod));
 module.hot.dispose(() => {
  const appRef: ApplicationRef = ngModule.injector.get(ApplicationRef);
  const elements = appRef.components.map(c => c.location.nativeElement);
  const makeVisible = createNewHosts(elements);
  ngModule.destroy();
  makeVisible();
 });
};

import { enableProdMode } from "@angular/core";
import { platformBrowserDynamic } from "@angular/platform-browser-dynamic";

import { AppModule } from "./app/app.module";
import { environment } from "./environments/environment";

import { hmrBootstrap } from "./hmr";

if (environment.production) {
 enableProdMode();
}

const bootstrap = () => platformBrowserDynamic().bootstrapModule(AppModule);

if (environment.hmr) {
 if (module["hot"]) {
  hmrBootstrap(module, bootstrap);
 } else {
  console.error("HMR is not enabled for webpack-dev-server!");
  console.log("Are you using the --hmr flag for ng serve");
 }
} else {
 bootstrap().catch(err => console.log(err));
}

...
"build": {
 "builder": "@angular-devkit/build-angular:browser",
 "options": {
  "outputPath": "dist/ng6",
  "index": "src/index.html",
  "main": "src/main.ts",
  "polyfills": "src/polyfills.ts",
  "tsConfig": "src/tsconfig.app.json",
  "assets": ["src/favicon.ico", "src/assets"],
  "styles": ["src/styles.css"],
  "scripts": []
 },
 "configurations": {
  "hmr": {
   "fileReplacements": [
    {
     "replace": "src/environments/environment.ts",
     "with": "src/environments/environment.hmr.ts"
    }
   ]
  },
  "production": {
   "fileReplacements": [
    {
     "replace": "src/environments/environment.ts",
     "with": "src/environments/environment.prod.ts"
    }
   ],
   "optimization": true,
   "outputHashing": "all",
   "sourceMap": false,
   "extractCss": true,
   "namedChunks": false,
   "aot": true,
   "extractLicenses": true,
   "vendorChunk": false,
   "buildOptimizer": true
  }
 }
},
...
"serve": {
 "builder": "@angular-devkit/build-angular:dev-server",
 "options": {
  "browserTarget": "ng6:build"
 },
 "configurations": {
  "production": {
   "browserTarget": "ng6:build:production"
  },
  "hmr": {
   "browserTarget": "ng6:build:hmr",
   "hmr": true
  }
 }
},