语法:函数名(x=1,y=2){...},当不传入参数调用函数时，会使用默认设置的参数值
代码示例:
<html ng-app='app' ng-controller='main' >
<head>
<meta charset="utf-8">
<meta name='viewport' content='width=device-width,user-scalable=no,initial-scale=1.0,maximum-scale=1.0,minimum-scale=1.0'>
<script src='jq/jquery-3.4.1.js'></script>
<style>
</style>
</head>
<body >
<script>
function fun(x=1,y=2)
{
console.log(x+y);
}
fun();
</script>
</body>
</html>
