js怎么限制文本框input只能输入数字

1、说明
本篇文章介绍怎么使用js限制文本框只能输入数字
2、HTML代码
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <title></title>
    <script type="text/javascript">
        function validationNumber(e, num) {
            var regu = /^[0-9]+.?[0-9]*$/;
            if (e.value != "") {
                if (!regu.test(e.value)) {
                    alert("请输入正确的数字");
                    e.value = e.value.substring(0, e.value.length - 1);
                    e.focus();
                } else {
                    if (num == 0) {
                        if (e.value.indexOf('.') > -1) {
                            e.value = e.value.substring(0, e.value.length - 1);
                            e.focus();
                        }
                    }
                    if (e.value.indexOf('.') > -1) {
                        if (e.value.split('.')[1].length > num) {
                            e.value = e.value.substring(0, e.value.length - 1);
                            e.focus();
                        }
                    }
                }
            }
        }

</script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <input type="text" onkeyup="validationNumber(this,0)" name="id1" value="" />
    </div>
    </form>
</body>
</html>