关于js中按钮类型是image时表单验证问题---点击一次可以验证再次点击直接提交--的问题

function _submit(){ var tableForm = document.getElementById("jvForm"); tableForm.action="${base}/coursequestion/inner_super/o_update.jspx"; tableForm.onsubmit=null;  tableForm.submit(); }function _check(){ var reg = new RegExp("^[A-D]+$");   var answer = document.getElementById("answer").value; if(!reg.test(answer)){   alert("答案格式不对！");   return false;     }  _submit(); return true;}<form id="jvForm" method="post" onsubmit="return _submit();"><input type="image" src="/${res}/images/submit.gif" value="submit" onclick="return _check()"/>

问题顺利解决了！