Edit in JSFiddle

var Conference = function( name ) {
    this.name = name;
    this.attendees = [];
};

Conference.prototype.register = function( e ) {
    var $attendee = $( $( e.target ).data( "target" ) );
    
    this.attendees.push( $attendee.val() );

    alert( "Thanks for registering for " + this.name + ". " + 
          "There are " + this.attendees.length + " registered thus far." );
    
    $attendee.val( "" );
};

var conference = new Conference( "JavaScript Code Camp" );

$( document ).ready( function() {
    $( "#register" ).on( "click", $.proxy( conference.register, conference ) );
});

<label for="attendee-name">Attendee Name</label>
<input id="attendee-name" type="text"></input>
<button id="register" data-target="#attendee-name">Register</button>