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Private variables can only be accessed from methods that are declared inline, and not externally referenced or created using the prototype construct. Methods of this kind are also known as privileged methods

prototype chain.

That also means that if the mycircle prototype is changed (properties are added or deleted, etc.), these changes are replicated down the chain, so the mysphere also inherits these changes.

mysphere.prototype.constructor = mysphere;

I will take all of the methods out of the constructor, and add them later using the prototype. That way, the mycircle prototype methods will always be available without me needing to create a new mycircle. Unfortunately, this also means that public and private properties are very hard (or impossible) to use. It's a trade off - one functionality for another.

When running the method, we need to tell JavaScript that even though we are referencing a method for a different prototype, we want to run it as if it were a method of the object we are creating (to make sure that any properties it creates are added to the object we are creating). This could be done using the 'call' method or 'apply' method

Note that when assigning the mycircle object to the mysphere prototype, it also overwrites the mysphere prototype constructor property