Knockout Table Checkbox Binding

HTML

<h4>Employees:</h4>
<table>
    <thead>
        <tr><th>Select</th><th>First name</th><th>Last name</th><th>Role</th></tr>
    </thead>
    <tbody data-bind="foreach: $root.employees">
        <tr>
            <td><input type="checkbox" data-bind="value: id(), click: $root.toggleAssociation" /></td>
            <td><span data-bind="text: name"></span></td>
            <td><span data-bind="text: sname"></span></td>
            <td><span data-bind="text: role"></span></td>
        </tr>
    </tbody>
</table>

<h4>Selected co-workers:</h4>
<div data-bind="foreach: $root.selectedEmployees">
    <span data-bind="text: name() + ' ' + sname()"></span>
    <br/>
</div>
<div>
  
    <button data-bind="click: save">Valider</button>
</div>

JavaScript

function Employee(id, name, sname, role) {
    var self = this;

    self.id = ko.observable(id);
    self.name = ko.observable(name);
    self.sname = ko.observable(sname);
    self.role = ko.observable(role);
    
    self.Selected = ko.observable(false); // if checked or not
}

function ViewModel() {
    var self = this;

    self.employees = ko.observableArray();
    
    self.selectedEmployees = ko.computed(function() {
        return self.employees().filter(function(item) {
            return item.Selected();
        });
    });                              

    self.init = function () {
        self.employees.push(new Employee(1, 'Tom', 'Jones', 'Manager'));
        self.employees.push(new Employee(2, 'James', 'Bond', 'Designer'));
        self.employees.push(new Employee(3, 'Darren', 'Wright', 'Developer'));
    };
    
    self.toggleAssociation = function (item) {
  
       item.Selected(!(item.Selected()));
       
        return true;
    };
    self.save = function() {
      
    	var txt="";
      var tab =self.selectedEmployees();
      for(i=0;i<	self.selectedEmployees().length;i++)
      {
      txt = txt+" "+self.selectedEmployees()[i].id();
      }
 
   alert(txt);
    };
}

var viewModel = new ViewModel();
ko.applyBindings(viewModel);
viewModel.init();