inheritance ? (how to do it in javascript)

I'm kinda new to Javascript and scripting in general, but I have been programming in c++ a couple of years ago, so I did things kinda different than I'm doing now in Unity, so I may be asking weird things.

I made a script to control the playercharacter (in javascript), but now I want to make a script for an npc, and I want it to be a sub-class of the player class (well actually I want to make a baseclass (superclass) and have both the player and npc inherit from it)

but how do I that ? I never actually declare any class, I just start writing in seperate scripts as if those are classes.

I tried: public class NPCBoarderScript : PlayerScript but that doesn't work