js、checkbox求助
现有代码

function dsubmitStory(){

????if($("#u_tag").val()?==""?||?$("#u_tag").val()?=="最少要入兩個標籤,用“,”分隔"){

????????alert("標籤不能為空!");

????????return?false;

????}else{

????????var?t?=?$("#u_tag").val().split(",");

????????if(t.length<2){	

????????????alert("請最少輸入兩個標籤！");

????????????return?false;

????????}else?if(t.length>=2&&t.length<=3){

????????????for(var?j=0;j<t.length;j++){

????????????????if(t[j].length>20){

????????????????????alert("標籤長度不能超過20!");

????????????????????return?false;

????????????????}

????????????}

????????}else?if(t.length>3){

????????????alert("最多只能輸入三個標籤!");

????????????return?false;

????????}

????????//验证通过执行

????????//document.addStory.submit();?

????}

	document.addStory.submit();?

}

以及

<c:forEach var="p" items="${TagList}" varStatus="vs">

	                            <td  valign="top">

	                            <c:if test="${vs.index!=0}"><div class="form-ul-left"></div></c:if>

	                                <div class="form-ul-div">

	                                    <ul class="form-ul">

	                                        <li><input class="form-ul-li-input" type="checkbox" value="${p.id}" name="ftagid" id="t_${p.id}">${p.tag}</li>

	                                    </ul>

	                                </div>

	                            </td>

                            </c:forEach>

现在我想要在js里面加上对checkbox的验证，条件是至少选择一个复选框，否侧弹出验证不通过的提示，自己弄了一下午了，求助啊
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