import { PLATFORM_ID } from '
@angular/core';
 import { isPlatformBrowser, isPlatformServer } from '
@angular/common'; 
 constructor(
@Inject(PLATFORM_ID) private platformId: Object) { ... } 
 ngOnInit() {
   if (isPlatformBrowser(this.platformId)) {
      // Client only code.
      ...
   }
   if (isPlatformServer(this.platformId)) {
     // Server only code.
     ...
   }
 }