Angularjs extends service
At first sight, your code is short and there is nothing wrong with it.

At second sight, there are a few things to improve:


Your semicolons are all over the place; you have both missing and pointless semicolons.
There is no point in declaring id in all since you clearly will not use it
ngPost is an old skool constructor, it's name really should start with an uppercase


These things I gleaned from JSHint, you should use it.

Furthermore, I could be wrong, it seems that you are mixing functions which I would put in posts together with functions which I would put in post. I am not sure that is the best approach.