<!DOCTYPE html>
<html>
<body>
<h1>默认参数值</h1>
<p id="demo"></p>
<script>
function myFunction(x, y = 10) {
// 如果未通过或未定义，则 y 为 10
return x + y;
}
document.getElementById("demo").innerHTML = myFunction(5);
</script>
</body>
</html>