plugin.js

import { Injectable } from '@angular/core';
import { Diagnostic } from '@ionic-native/diagnostic';

@Injectable()
export class CheckHardwareProvider {
  
  /**
   * @param diagnostic
   */
  constructor(
    private diagnostic: Diagnostic
  ) {
    console.log('Hello CheckHardware Provider');
  }

  public stateWifi() {
    this.diagnostic.isWifiAvailable().then(available => {
      if( ! available ) {
        this.diagnostic.switchToWifiSettings();
      }
    },
    error => {
      alert(JSON.stringify(error));
    })
  }
}