Native-Plugin installed but not found Error

I am new in Ionic and Angular. i created a ionic 3 app in visual code. App works fine , but whenever i try to install any native plug in like camera and all it’s giving error. Later i found that not only ionic-native plug in any npm-install giving that error.

C:\AngularProjects\SideMenuAPP\SideMenuAPP>npm install chart.js --save
SideMenuAPP@0.0.1 C:\AngularProjects\SideMenuAPP\SideMenuAPP
`-- chart.js@2.6.0
  +-- chartjs-color@2.1.0
  | +-- chartjs-color-string@0.4.0
  | `-- color-convert@0.5.3
  `-- moment@2.18.1

npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@^1.0.0 (node_modules\chokidar\node_modules\fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.1.2: wanted {"os":"darwin","arch":"any"} (current:
 {"os":"win32","arch":"x64"})
npm WARN ajv-keywords@2.1.0 requires a peer of ajv@>=5.0.0 but none was installed.

C:\AngularProjects\SideMenuAPP\SideMenuAPP>

What is the error? I only see (harmless) warnings.
What is not working as it should?

Sorry , i thought because of this warning plugins are not installing successfully .
I am just exploring all Native plugins to test how it works, but in some cases error coming that “plug in not installed”.
This one giving error for google-plugin ,

undefined
"Native: tried calling GooglePlus.login, but the GooglePlus plugin is not installed."
"Install the GooglePlus plugin: 'ionic cordova plugin add cordova-plugin-googleplus'"

import { Component } from '@angular/core';
import { NavController } from 'ionic-angular';
import { ProfilePage } from '../profile/profile';
import { GooglePlus } from '@ionic-native/google-plus';
import firebase from 'firebase';


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

  userProfile: any = null;
  constructor(public navCtrl: NavController,private googlePlus: GooglePlus) {
    try {
      firebase.auth().onAuthStateChanged( user => {
    if (user){
      this.userProfile = user;
    } else { 
      this.userProfile = null; 
    }
  });
      
    } catch (error) {
      console.log(error);      
    }
  
}
loginUser(): void {
  this.googlePlus.login({
    'webClientId': '******************************************************',
    'offline': true
  }).then( res => console.log(res))
    .catch(err => console.error(err));
}

  goto(){
    this.navCtrl.push(ProfilePage,{item:""});
  }
}

app.module.ts
-------------------
import { BrowserModule } from '@angular/platform-browser';
import { ErrorHandler, NgModule } from '@angular/core';
import { IonicApp, IonicErrorHandler, IonicModule } from 'ionic-angular';

import { MyApp } from './app.component';
import { HomePage } from '../pages/home/home';
import { ListPage } from '../pages/list/list';
import { ProfilePage } from '../pages/profile/profile';
import { DetailsPage } from '../pages/details/details';
import { HttpModule } from '@angular/http';
import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';
import { Camera } from '@ionic-native/Camera';
import { SQLite, SQLiteObject } from '@ionic-native/sqlite';
import { GooglePlus } from '@ionic-native/google-plus';

@NgModule({
  declarations: [
    MyApp,
    HomePage,
    ListPage,
    ProfilePage,
    DetailsPage
  ],
  imports: [
    BrowserModule, HttpModule,
    IonicModule.forRoot(MyApp),
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    HomePage,
    ListPage,
    ProfilePage,
    DetailsPage
  ],
  providers: [
    StatusBar,
    SplashScreen,
    Camera,    
    SQLite,
    GooglePlus,
    { provide: ErrorHandler, useClass: IonicErrorHandler }
  ]
})
export class AppModule { }

When i reinstalling google plugin it showing this

C:\AngularProjects\SideMenuAPP\SideMenuAPP>ionic cordova plugin add cordova-plugin-googleplus --variable REVERSED_CLIENT_ID=****************************
> cordova plugin add cordova-plugin-googleplus --variable REVERSED_CLIENT_ID=**************************** --save
√ Running command - done!
Plugin "cordova-plugin-googleplus" already installed on android.
Saved plugin info for "cordova-plugin-googleplus" to config.xml

C:\AngularProjects\SideMenuAPP\SideMenuAPP>npm install --save @ionic-native/google-plus
SideMenuAPP@0.0.1 C:\AngularProjects\SideMenuAPP\SideMenuAPP
`-- @ionic-native/google-plus@4.1.0

npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@^1.0.0 (node_modules\chokidar\node_modules\fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.1.2: wanted {"os":"darwin","arch":"any"} (current:
 {"os":"win32","arch":"x64"})
npm WARN ajv-keywords@2.1.0 requires a peer of ajv@>=5.0.0 but none was installed.

And the big issue is ,this problem is inconsistent , not happening with all plugin, camera is working fine. pls help

Uninstall it first with remove instead of add and try to add again.