<!DOCTYPE html>
<html>
<body>
<h2>JavaScriptオブジェクトのプロパティ/h2>
<p>既存のオブジェクトに新しいプロパティを追加します。</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 + " は " + person.nationality + "。";
</script>
</body>
</html>
