So, here’s situation, today my friend get attacked by a npc thug, he try to hide in the house and close the door, and then NPC open it and start shooting, then he died.
my friend just ask me why there’s no option that player can lock the door, anyone plan to make one?
It’s basically just a map coding problem at this point. As of the moment I know that at least I am holding off on bigger map changes (and I’m sure others are as well) to make the Z-levels changes and design a bit easier for Coolthulu to get done and into the game. Be assured that we’ve at least had a few discussions about how we could potentially handle things like this. 
Couldn’t one actually create an item that works like a reverse-crowbar? Using it on closed doors would lock it. I’m guessing the way prying works is by replacing the actual door-tile? Or do doors have a locked-property?
The problem is, all locked doors are identical. You can’t have keys to one locked door.
Additionally, doors are locked only from outside.
We can add something to let the player re-lock the door, but to get back in they’d need to pick the lock or force the door with a crowbar again. Just because they opened it once doesn’t mean they can open it again on demand. You’re right that we simply replace the “locked door” tile with an “unlocked door” tile.
We could probably add keys somewhere in the house though, or elsewhere for that matter. It would be nice to reward carefully breaking in instead of smashing your way in.
We could add keys, the key would say which door it unlocked instead of the other way around.
In fact, it would probably be reasonable for there to be one key per house, that wouldn’t be much harder.
Maybe just add an option to the Construction menu, whereas you could block the door with chairs, dressers and alike; supposedly, all the doors should be the same & single-built, swiniging open inside the room.
Just drag furniture next to closed doors, it already works.