Defining and inheriting from a Javascript Class

Here's my problem:

Every object in my game has an "ObjectScript.js" which defines the properties of that object. This script has a function called "MyAction" which defines what that particular object should do.

I want to create a unique script for every object type that inherits its properties from ObjectScript.js but override the "MyAction" function with custom script.

Example: ObjectScript.js (Defines properties and functions of all objects)

---function MyAction(){...defines default function}

Character.js - inherits from ObjectScript.js

---function MyAction() {...overrides the default script in the inherited function}

Seems like this should be easy and I have seen a few examples but I just not understanding it. Can anyone give me an example of how this works or suggest a better method for inheriting script functions?

Thanks in advance.