interface House { sqft: number; yard?: { sqft: number; }; } function printYardSize(house: House) { const yardSize = house.yard?.sqft; if (yardSize === undefined) { console.log('No yard'); } else { console.log(`Yard is ${yardSize} sqft`); } } let home: House = { sqft: 500 }; printYardSize(home); // Prints 'No yard'