Edit in JSFiddle

var contacts = new Backbone.Collection([
    {firstName: 'John',lastName: 'Doe',phone: '111-111-1111'}, 
    {firstName: 'Jane',lastName: 'Doe',phone: '222-222-2222'},
],{model:Backbone.Model});
    
console.log(JSON.stringify(contacts.toJSON())); //check current model attributes
    
//add Bill Doe, Remove Jane Doe, Update John Doe
contacts.set([
    {firstName: 'Bill',lastName: 'Doe',phone: '333-333-3333'}, 
    {firstName: 'Jane', middleName: 'Roe', lastName: 'Doe',phone: '555-555-5555'}
]);
//verify changes
console.log(JSON.stringify(contacts.toJSON()));