interface Person { name: string; age: number; } const person: Person = { name: "John Doe", age: 30 }; if (person instanceof Person) { console.log("object is of interface type!"); } else { console.log("object is not of type Person interface"); } // An "interface" is a TypeScript concept, and does not exist during run-time. You cannot check if an obeject is of type interface. // You can, however, check if an object is shaped like your interface: interface User { firstName: string lastName: string } function isUser(v: any): v is User { return typeof v === 'object' && v !== null && typeof v.firstName === 'string' && typeof v.lastName === 'string' } const u: unknown = // something unknown if (isUser(u)) { // TypeScript will recognize `u` is now a `User` interface }