When a property is accessed on an object and if the property is not found on that object, the JavaScript engine should looks at the object's __proto__(different browser has their own implement) .Or, looks at the prototype of its constructor.

In 4. Greatest Common Divisor of JS: Interview Algorithm part -1: beginner, you mentioned a fancy algorithm that you don't understand.

It is called Euclidean Algorithm. I am thinking that you probably should give a link here so that readers can read and understand. You can link to the Wikipedia