Is there any substantial difference in doing either of these?

```
delete a.x;

```

vs

```
a.x = undefined;

```

where 

```
a = {
    x: 'boo'
};

```

could it be said that they are equivalent?

(I'm not taking into account stuff like ["V8 likes not using `delete` better"](http://coding.smashingmagazine.com/2012/11/05/writing-fast-memory-efficient-javascript/))