Get domain name for service in Angular2

Another option is to use DOCUMENT from @angular/platform-browser.

import {DOCUMENT} from '@angular/platform-browser';

constructor(@Inject(DOCUMENT) private document: Document) {
    let url = document.location.protocol +'//'+ document.location.hostname + ':my_port' );
}

Angular 2 latest working solution:

app.module.ts

providers: [
    {provide: Window, useValue: window},
    ...
]

youclass.ts

constructor(
    @Inject(Window) private _window: Window
) {
    this._baseUrl = `http://${this._window.location.hostname}:3333`;
};

There's no need for an angular2-specific solution. You can use the window.location.hostname to get the current hostname.

Note, however, if you don't want to use global variables like the window-object directly, you can provide your own Window object, which then can be injected.

See this full working Stackblitz Angular sample for details.

Updated Answer for Angular 6+

As others have stated, the original answer does not work anymore. For Angular 6+, you need to provide an Injection Token, so that the window-object can be resolved in the AOT-build too. Otherwise you will get the error "Can't resolve all parameters".

I recommend creating a WINDOW_PROVIDERS array in a separate file like this:

import { InjectionToken, FactoryProvider } from '@angular/core';

export const WINDOW = new InjectionToken<Window>('window');

const windowProvider: FactoryProvider = {
  provide: WINDOW,
  useFactory: () => window
};

export const WINDOW_PROVIDERS = [
    windowProvider
]

The WINDOW_PROVIDERS constant can be added to the providers array in the AppModule like this:

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [
    WINDOW_PROVIDERS, // <- add WINDOW_PROVIDERS here
    SampleService,
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

In the SampleService, the window object can be injected by using the defined Injection Token like this:

import { Injectable, Inject } from '@angular/core';
import { WINDOW } from '../window.provider';

@Injectable()
export class SampleService {

    constructor(@Inject(WINDOW) private window: Window) {
    }

    getHostname() : string {
        return this.window.location.hostname;
    }
}

Original Answer for Angular 2

Therefore you need to set the provider for the Window-object when bootstrapping your application.

import {provide} from 'angular2/core';
bootstrap(..., [provide(Window, {useValue: window})]);

After that you can use the window object and access the hostname like this:

constructor(private window: Window) {
   var hostname = this.window.location.hostname;
}