Rule 8.14

A constructor’s parameter property (constructor(public x: f32), or private, protected or readonly in place of public) is a field of its class, at the constructor’s place among the members, which the constructor assigns from the parameter before the field initializers run. A field written without a type must take the type its initializer names (a written number is an f32 by Rule 5.1, true and false a bool, new C() the struct C, and a type’s own constructor that type), and a field whose initializer names none, or that has neither, must be refused. A readonly field may be assigned only in a constructor of the class that declares it, which is TypeScript’s rule; readonly is shallow, as TypeScript’s is, so a write into what the field holds stands. Field initializers must run in TypeScript’s order: those of the classes above the class whose constructor runs first (in the base constructor its super(...) calls, or before its body when none of them has one), that class’s parameter properties and its own after super(...) returns, and those of the classes below it when its body returns, so an initializer a derived class writes for an inherited field runs last.