console 命令行工具 X clear
console
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script>
        window.onload = function() {
            var oAA = document.createElement("input");        
            document.body.appendChild(oAA);         
            oAA.type = "button";
            oAA.value = "按钮2";
            oAA.id = "btn";
        }
    </script>
</head>
<body>
</body>
</html>