JavaScript 控制文本框的值连续加减

<title>javascript控制文本框的值连续加减</title> <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"> <form runat="server"> <input id="textbox1" runat="server" width="50" cssclass="mybutton" text="0"><input type="button" id="button1" value="＋" onmousedown="md(this)" onmouseout="mo(this)" onmouseup="mo(this)"><input type="button" id="button2" value="－" onmousedown="md(this)" onmouseout="mo(this)" onmouseup="mo(this)"> </form>
[ctrl+a 全选 注:如需引入外部js需刷新才能执行]