Nominal typing with correct variance describes OO (classes, inheritance and rules governing it <<liskov substitution principles, L from SOLID>>). Structural typ

Nominal typing with correct variance describes OO (classes, inheritance and rules governing it <<liskov substitution principles, L from SOLID>>). Structural typing is used for everything else in js. Flow does it correctly. Typescript treats everything as structurally typed. As a side note flow also has first class support for opaque types so no need to resort to branding hacks.