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<!DOCTYPE html> <html> <body> <h2>JavaScript Object Properties</h2> <p>Add a new property to an existing object:</p> <p id="demo"></p> <script> const person = { firstname: "John", lastname: "Doe", age: 50, eyecolor: "blue" }; person.nationality = "English"; document.getElementById("demo").innerHTML = person.firstname + " is " + person.nationality + "."; </script> </body> </html>