JSFiddle - React, Tailwind, and code Playground

HTML

<div ng-controller='TravelController' ng-init='init()'>

Countries <select ng-model='TravelToCountryId'     
    ng-options='i.CountryId as i.CountryName for i in countries' 
    
    ng-init='filterCitiesByCountry()'
    ng-change='filterCitiesByCountry()'></select>
    
<br/>
Cities <select id='TravelToCityId'
    ng-model='TravelToCityId'
    ng-options='i.CityId as i.CityName for i in citiesFromSelectedCountry'
    ></select>


    <hr/>
 
    
    Travel To    <br/>
    Country Id: {{TravelToCountryId}}    <br/>
    City Id: {{TravelToCityId}}    <br/>
    
</div>

JavaScript

function TravelController($scope) {
    
    // Models
    
    $scope.countries = 
    [
        { 
            CountryId: 1, CountryName: 'Philippines',
            Cities :
            [
                { CityId: 1, CityName: 'Manila' },
                { CityId: 2, CityName: 'Makati' },
                { CityId: 3, CityName: 'Quezon' },            
            ]            
        },
        { 
            CountryId: 2, CountryName: 'Canada',
            Cities:
            [
                { CityId: 4, CityName: 'Toronto' },
                { CityId: 5, CityName: 'Alberta' },
                { CityId: 6, CityName: 'Winnipeg' },
            ]           
            
        },
        { 
            CountryId: 3, CountryName: 'China',
            Cities:
            [
                { CityId: 7, CityName: 'Beijing' },
                { CityId: 8, CityName: 'Shanghai' }
            ]           
        },    
    ];    
    
    $scope.TravelToCountryId = null;
    $scope.TravelToCityId = null;
    
    
    // Controller's actions
    
    $scope.init = function() {
        $scope.TravelToCountryId = $scope.countries[1].CountryId;    
    };
        
    
    $scope.filterCitiesByCountry = function() {
        
       
        var cities = $scope.citiesFromSelectedCountry = $scope.countries.filter(function(v){
            return v.CountryId == $scope.TravelToCountryId; 
        })[0].Cities;


        
        $scope.TravelToCityId = cities[0].CityId;        
        
        
    };
        
        
}