angular6 feature module lazy loading throwing error TypeError: undefined is not a function

Question

I have this code in app-routing.module.ts, as per the new documentation in angular I went through the method still it's not working, throwing some errors I can't understand.

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { RouterModule, Routes } from "@angular/router";
import { HomeComponent } from "./home/home.component";
import { AdminModule } from "./admin/admin.module";

const routes: Routes = [
  {
    path: 'admin',
    loadChildren: './admin/admin.module#AdminModule'
  },
  { path: '', redirectTo: '/home', pathMatch: 'full' },
  { path: 'home', component: HomeComponent },
];

@NgModule({
  imports: [
    CommonModule,
    RouterModule.forRoot(routes)
  ],
  exports: [
    RouterModule
  ],
  declarations: []
 })
 export class AppRoutingModule { }

It's throwing an error like this.

I have also tried the old way of loadchildren like this 'app/admin/admin.module#AdminModule'. But it's still not working.

core.js:1601 ERROR Error: Uncaught (in promise): TypeError: undefined is not a function
TypeError: undefined is not a function
    at Array.map (<anonymous>)
    at webpackAsyncContext ($_lazy_route_resource lazy namespace object:18)
    at SystemJsNgModuleLoader.push../node_modules/@angular/core/fesm5/core.js.SystemJsNgModuleLoader.loadAndCompile (core.js:5569)
    at SystemJsNgModuleLoader.push../node_modules/@angular/core/fesm5/core.js.SystemJsNgModuleLoader.load (core.js:5561)
    at RouterConfigLoader.push../node_modules/@angular/router/fesm5/router.js.RouterConfigLoader.loadModuleFactory (router.js:3294)
    at RouterConfigLoader.push../node_modules/@angular/router/fesm5/router.js.RouterConfigLoader.load (router.js:3282)
    at MergeMapSubscriber.project (router.js:1479)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber._tryNext (mergeMap.js:117)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber._next (mergeMap.js:107)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:93)
    at Array.map (<anonymous>)
    at webpackAsyncContext ($_lazy_route_resource lazy namespace object:18)
    at SystemJsNgModuleLoader.push../node_modules/@angular/core/fesm5/core.js.SystemJsNgModuleLoader.loadAndCompile (core.js:5569)
    at SystemJsNgModuleLoader.push../node_modules/@angular/core/fesm5/core.js.SystemJsNgModuleLoader.load (core.js:5561)
    at RouterConfigLoader.push../node_modules/@angular/router/fesm5/router.js.RouterConfigLoader.loadModuleFactory (router.js:3294)
    at RouterConfigLoader.push../node_modules/@angular/router/fesm5/router.js.RouterConfigLoader.load (router.js:3282)
    at MergeMapSubscriber.project (router.js:1479)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber._tryNext (mergeMap.js:117)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber._next (mergeMap.js:107)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/Subscriber.js.Subscriber.next (Subscriber.js:93)
    at resolvePromise (zone.js:814)
    at resolvePromise (zone.js:771)
    at zone.js:873
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:421)
    at Object.onInvokeTask (core.js:4062)
    at ZoneDelegate.push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:420)
    at Zone.push../node_modules/zone.js/dist/zone.js.Zone.runTask (zone.js:188)
    at drainMicroTaskQueue (zone.js:595)
    at ZoneTask.push../node_modules/zone.js/dist/zone.js.ZoneTask.invokeTask [as invoke] (zone.js:500)
    at invokeTask (zone.js:1540)

Answer 1

I had the same problem, the cause for me was that i was importing the lazy loaded module in my app module.

Answer 2

This error is firing after some recompilation when ng serve is running, and after that, it shows always. Restarting ng serve - solved this problem.

Important!

Using loadChildren as function - is Not lazy loading:

{path: 'admin', loadChildren:() => AdminModule } //not lazy loading

cause you need to import the lazy module in the routing module.

For Lazy loading, you must send the path to the lazy module - as String!

{path: 'admin', loadChildren:'app/admin/admin.module#AdminModule'} // This is lazy loading