function checkNumber(e)
{
var key = window.event ? e.keyCode : e.which; var keychar = String.fromCharCode(key); var el = document.getElementById('test'); var msg = document.getElementById('msg'); reg = //d/; var result = reg.test(keychar); if(!result) 
{
el.className = "warn"; msg.innerHTML = "只能输入数字"; return false; 
} else { el.className = ""; msg.innerHTML = ""; return true; } 
}
<div id="test"> 问题序号所在页码 <input type="text" name="question.page" onkeypress="return checkNumber(event);"> <span id="msg"></span> </div>