Edit in JSFiddle

var person = {
    firstName: 'John',
    lastName: 'Papa',
    changeMyName: function(){
        this.firstName = $('#nameTxt').val();
    }
    };

//extend the person with an age property
person.age = 21;

var displayName = function() {
    $('#msg').text(person.firstName);
};


// display the name
displayName();

$('#btn').click(function() {
    //change the name to Brad
    person.changeMyName();
    displayName();
});

<div>
    <input text="John" id="nameTxt"/>
    <button id="btn">Change it</button>
</div>

<p>Name: <span id="msg"></span></p>