JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.0.7/angular.min.js"></script>
<div id="app1" ng-controller="App1Ctrl">
  <button ng-click="change()">Change</button>
  {{ text() }}
</div>

<div id="app2" ng-controller="App2Ctrl">
  <button ng-click="change()">Change</button>
  {{ text() }}
</div>

JavaScript

angular.module('test-service', [])
  .service('TestService', function($window){
    var text = 'Initial state';

    if (!!$window.sharedService){
      return $window.sharedService;
    }

    $window.sharedService = {
      change: function(newText){
        text = newText;
      },
      get: function(){
        return text;
      }
    }

    return $window.sharedService;
  });

angular.module('app1', ['test-service'])
  .controller('App1Ctrl', function($scope, TestService){
    $scope.text = function(){ return TestService.get() }
    $scope.change = function(){ TestService.change('app 1 activated') }
  });

angular.module('app2', ['test-service'])
  .controller('App2Ctrl', function($scope, TestService){
    $scope.text = function(){ return TestService.get() }
    $scope.change = function(){ TestService.change('app 2 activated') }
  });

var app1El = document.getElementById('app1');
var app2El = document.getElementById('app2');

angular.bootstrap(app1El, ['app1', 'test-service']);
angular.bootstrap(app2El, ['app2', 'test-service']);