buggy.js

var Widget = function(){
   this.messages = [];
};

Widget.prototype.type='Widget';

var SubWidget = function( name ){
  
  this.name = name;

};

SubWidget.prototype = new Widget();

buggy2.js

var sub1 = new SubWidget( 'foo' );
var sub2 = new SubWidget( 'bar' );

sub1.messages.push( 'foo' ); 
sub2.messages.push( 'bar' );

fixed.js

var Widget = function(){
   this.messages = [];
};

Widget.prototype.type='Widget';

var SubWidget = function( name ){
  
  this.name = name;

  Widget.apply( this, Array.prototype.slice.call(this) );
};

SubWidget.prototype = new Widget();