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>