JSFiddle - React, Tailwind, and code Playground

HTML

<div ng-app="myApp">
    <div ng-controller="MyCtrl">
        <div ng-click="setFTag()">Click Me</div>
    </div>
</div>

JavaScript

var myApp = angular.module('myApp',[]);

myApp.service('myService', function() {
    this.tags = {
        a: true,
        b: true
    };
    
    
    this.setFalseTag = function() {
        //alert("Within myService->setFalseTag");
        this.tags.a = false;
        this.tags.b = false;
        
        //how do I get the watch in MyCtrl to be triggered?
    };
});


myApp.controller('MyCtrl', function($scope, myService) {
    
    //$scope.myService = myService;
    
    $scope.setFTag = function() {
        //alert("Within MyCtrl->setFTag");
        myService.setFalseTag();
    };        
    
    $scope.$watch(function () {
    alert('hello')
    return myService.tags;
}, 
                  
      function(newVal, oldVal) {
        alert("Inside watch");
        console.log(newVal);
        console.log(oldVal);
    }, true);
    
});