error.js

class MyError extends Error {
  constructor() {
    super();
  }
}

class YourError extends MyError {
  constructor() {
    super();
  }
}

try {
  throw new MyError();
} catch (e) {
  switch (e.constructor) {
    case YourError: console.log("Was instance of your error!"); break;
    case MyError: console.log("Was instance of my error!"); break;
    default: console.log("Unknown error type!"); break;
  }
}

try {
  throw new YourError();
} catch (e) {
  switch (e.constructor) {
    case MyError: console.log("Was instance of my error!"); break;
    case YourError: console.log("Was instance of your error!"); break;
    default: console.log("Unknown error type!"); break;
  }
}