Error: No provider for HttpHandler in angular2

Add HttpClientModule to your imports[] in app.module.ts. This might be one of the mistakes.

HttpClient is introduced in angular 4.3,so if you want to use HttpClient you need to import HttpClientModule from '@angular/common/http'. Make sure to import HttpClientModule after BrowserModule as shown below. This official doc and so answer will give you indepth information.

import { HttpClientModule } from '@angular/common/http';

@NgModule({
 imports: [
   BrowserModule,
   HttpClientModule
 ],
 ...