IMO it lends itself to patterns like:
Not only are you doing extra branching, but by having defaults at the usage site instead of defaults site you could have inconsistencies.
Instead, on construction of the this, you could have
and then access all the properties unconditionally.
(You could also only merge in properties that already exist in defaultData tree, and perform validation at this stage, creating a very predictable this)
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.