I'm glad someone adds "var" or "let".

Is it an actual best practice?

By adding a method directly into a constructor, the method is copied every time you create a new instance.
That's why it's better to add it using

Ship.prototype.isWorthIt = function(){}

outside the constructor, or by using ES6 classes.

Great!thx!

Great explanation, thank you!

Same in the javascript version.

Thanks for the feedback, the description has been updated.

It was not directly clear for me that floats need to be returned as NaN.
Only after the provided test with a float failed I noticed that I need to return NaN.