how to create function gameObject.myfunction(); ??

for example standard functions : /JS/gameObject.AddComponent(blabla); or …ToString();

i want create approximate function

gameObject.myfunction();

gameObject points to an Object of type GameObject. GameObject is a class and as any class it has it’s own methods. You can’t add new methods to any of the built-in Unity classes unless you buy the source code of the engine.