¿Cuál es el resultado de la siguiente expresión?
let obj = {name: "John", age: 30}; obj["city"] = "London";
{name: "John", age: 30, [city]: "London"}
{name: "John", age: 30}
{name: "John", age: 30, city: "London"}
{name: "John", age: 30, "city": "London"}