Const keyword means constant, a value that won’t change after the application has been compiled; this allows for certain optimizations.
Let keyword is a JavaScript variable that is safely scoped down to the method or function level.
Var keyword is generally discouraged in JavaScript, because it’s a global declaration. The value of it could be available anywhere in the application, and the app might have collisions.
So, the meme is, shifting from a constant, unchanging gender, to the middle where gender is defined and scoped to a local level, to the extreme, where gender is variable globally.