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Via object composition, an object can contain other objects. For example, an Employee object might contain an Address object, along with other information like name and position. Composition is a "has-a" relationships, like "an employee has an address".

Inheritance be supported via the class or the prototype, which have differences but use similar terms like object and instance.

In class-based programming, the most common type of OOP, an object is an instance of a class. The class defines the data (variables) and methods (logic). An object is created via the constructor. Elements of class may include:

• Class variable – belongs to the class itself; all objects of the class share one copy

• Instance variable – belongs to an object; every object has its own version of these variables

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