import { Http } from '@angular/http';
import { Injectable } from '@angular/core';

@Injectable()
export class LoginServicesProvider {
  apiUrl: string = 'API URL COMES HERE';
  constructor(public http: Http) {
  }

  login(reqData) {
    this.http.post(apiUrl+'/checkLogin', reqData).map(res => res.json()).subscribe(data => {
      return data;
    });
  }

}

import { LoginServicesProvider } from './../../providers/login-services/login-services';
import { Http } from '@angular/http';
import { Component } from '@angular/core';
import { NavController, NavParams } from 'ionic-angular';
import { Observable } from 'rxjs/Observable';

@Component({
  selector: 'page-login-page',
  templateUrl: 'login-page.html',
})
export class LoginPage {

  loginServiceData: Observable<any>;
  constructor(public navCtrl: NavController,
    public navParams: NavParams,
    private http: Http,
    private loginService: LoginServicesProvider
    )
    {
        let userName: string = 'dumy_user_name';
        let userPassword: string = '12345';
        let data = {
            username: userName,
            password: userPassword,
        };

        this.loginServiceData = this.loginService.login(data);
        console.log(this.loginServiceData);
    }
}

cli packages: (C:UsersDemoAppDataRoamingnpmnode_modules)

    @ionic/cli-utils  : 1.19.0
    ionic (Ionic CLI) : 3.19.0

global packages:

    cordova (Cordova CLI) : not installed

local packages:

    @ionic/app-scripts : 3.1.2
    Cordova Platforms  : android 6.2.3 browser 5.0.3
    Ionic Framework    : ionic-angular 3.9.2

System:

    Android SDK Tools : 26.1.1
    Node              : v6.12.0
    npm               : 5.6.0
    OS                : Windows 10