<!DOCTYPE html>
<html>
<body>
<h1>将默认值设置为函数参数</h1>
<p id="demo"></p>
<script>
function myFunction(x, y) {
if (y === undefined) {
y = 0;
}
return x * y;
document.getElementById("demo").innerHTML = myFunction(4);
</script>
</body>
</html>