Object in If statement

Question

I'm quite new in this world so I apologise in advance if my question is not completely clear. I'm following an online course and I have this homework but I don't quite understand how to put my object element in my If Statement. After trying for hours I don't even know anymore if what I'm writing makes sense anymore. What I'm trying to achieve is my pop-up using the data from the "user" (which, for this homework, will be fake) to answer with the If statement. `

let weather = {
  paris: {
    temp: 19.7,
    humidity: 80,
  },
  tokyo: {
    temp: 17.3,
    humidity: 50,
  },
  lisbon: {
    temp: 30.2,
    humidity: 20,
  },
  "san francisco": {
    temp: 20.9,
    humidity: 100,
  },
  oslo: {
    temp: -5,
    humidity: 20,
  },
};


let city = prompt("Enter the city");
city = city.toLowerCase();
city = city.trim();
city = city.replace("sanfrancisco", "san francisco");

if (
  city === "tokyo" ||
  city === "paris" ||
  city === "lisbon" ||
  city === "san francisco" ||
  city === "oslo"
) {
  alert(`It's currently °C (°F) in ${city} with % of humidity.`);
} else {
  alert(
    "Sorry, we don't know the weather for this city, try going to https://www.google.com/search?q=weather+sydney"
  );
}

`

I also need to incorporate Math.round for the temperature but I don't know where to start.