export interface MyInterface { position?: any; test?: any; } class Doff implements MyInterface { // <-- ERROR 1 constructor() { // for the example it is direct assignment, // here is a loop that reads the fields and adds them 1 to 1 const field = "position" as keyof MyInterface; this[field] = true; // <<-- ERROR 2 } public four = 4; } console.log("OBJ >> ", new Doff()); /* > ERROR 1 Type 'Doff' has no properties in common with type 'MyInterface' > ERROR 2 Element implicitly has an 'any' type because expression of type 'keyof MyInterface' can't be used to index type 'Doff'. Property 'position' does not exist on type 'Doff'. */