undefined-example.js

let defineUser = {
  name: "Markus",
  age: 29,
  location: {
    country: "USA"
  }
}

if(typeof defineUser.location !== "undefined" && typeof defineUser.location.address !== "undefined") {
  console.log(defineUser.location.address);
}
else {
  console.log("No address is defined");
  if(typeof generateAddress !== "undefined") {
    generateAddress();
  }
}