代码示例:(标识:js_map_size)
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Map</h1>
<p>使用 Map.size:</p>

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

<script>
// 创建 Map
const fruits = new Map([
  ["apples", 500],
  ["bananas", 300],
  ["oranges", 200]
]);

document.getElementById("demo").innerHTML = fruits.size;
</script>

</body>
</html>
运行结果: