Communication between multiple viewmodels

vm1.js

	var self = this;
	self.firstName = ko.observable();
	self.lastName = ko.observable();
	self.fullName = ko.computed(function(){
		return self.firstName + " " + self.lastName;
	});
};

var viewModel2 = function(){
	var self = this;
	self.premium = ko.observable();
};

ko.applyBindings(new viewModel1(), document.getElementById("container1"));
ko.applyBindings(new viewModel2(), document.getElementById("container2"));

vm2.js

// view model 1 definition
var viewModel1 = function(){
 this.firstName = ko.observable("Wrapcode");
 this.messageForVM2 = ko.observable("Hello from first view model");
 this.message = ko.observable("Hello this is vm1")
};

//view model 2 definition
var viewModel2 = function(vm1){
 this.firstName = ko.observable(vm1.firstName());
 this.message = ko.observable(vm1.messageForVM2());
};

//master view model with instances of both the view models.
var masterVM = (function(){
 this.viewModel1 = new viewModel1(),
 this.firstName = "Rahul",
 this.viewModel2 = new viewModel2(this.viewModel1);
})();

ko.applyBindings(masterVM)

vm3.js

this.messageForVM2.subscribe(function(newValue) {
 shouter.notifySubscribers(newValue, "messageToPublish");
 });

vm4.js

shouter.subscribe(function(newValue) {
     this.message(newValue);
 }, this, "messageToPublish");