代码示例:(标识:js_set_add)
<!DOCTYPE html>
<html>
<body>

<h1>JavaScript Set</h1>

<p>向 Set 中添加新元素:</p>

<p id="demo"></p>

<script>
// 创建新的 Set
const letters = new Set(["a","b","c"]);

// 添加新元素
letters.add("d");
letters.add("e");

// 显示 set.size
document.getElementById("demo").innerHTML = letters.size;
</script>

</body>
</html>
运行结果: