js防止表单重复提交

<script language="javascript">       var checkSubmitFlg = false;       function checkSubmit() {             if (!checkSubmitFlg) {         checkSubmitFlg = true;             return true;          }else{         alert("不能重复提交");         return false;        }     }</script><form action="XXXX" method="POST"   onsubmit="return     checkSubmit()">  内容:<input type="text" name="content" value=""/><br>  <input type="submit" value="提交"><br></form>