Underscore's extend does not recursively copy child dependencies. This sucks if you want to create a deep copy of an object. This functionality doesn't exist.

underscore_objec_deep_copy

var _ = require( 'underscore');

var obj1 = {
  item : {
    yolo : {
      swag : {
        trill : true      
      }
    }
  }
};

var obj2 = _.extend({}, obj1);

console.log( 'obj1 === obj2:', obj1 === obj2 );
console.log( 'obj1.yolo === obj2.yolo:', obj1.yolo === obj2.yolo );

try {
  console.log( 'obj1.yolo.swag === obj2.yolo.swag:', obj1.yolo.swag === obj2.yolo.swag );
} catch( e ){
  console.log( 'obj1.yolo.swag === obj2.yolo.swag: exception' );
}

try {
  console.log( 'obj1.yolo.swag.trill === obj2.yolo.swag.trill:', obj1.yolo.swag === obj2.yolo.swag );
} catch( e ){
  console.log( 'obj1.yolo.swag.trill === obj2.yolo.swag.trill: exception' );
}