javascript object access performance

In Javascript, when your getting a property of an object, is there a performance penalty to getting the whole object vs only getting a property of that object?

Also Keep in mind I'm not talking about DOM access these are pure simple Javascript objects.

For example:

Is there some kind of performance difference between the following code:

Assumed to be faster but not sure:

var length = some.object[key].length;

if(length === condition){
  // Do something that doesnt need anything inside of some.object[key]
}
else{
  var object = some.object[key];
  // Do something that requires stuff inside of some.object[key]
}

I think this would be slower but not sure if it matters.

var object = some.object[key];

if(object.length === condition){
  // Do something that doesnt need anything inside of some.object[key]
}
else{
  // Do something that requires stuff inside of some.object[key]
}