用js写留言信息的判断非空条件

<form action="{:U('validate')}" method="post" name="myform">                              <input type="hidden" name="lanmu" value="33">                              <li>                                <div class="main_ly_t1"><em>留言标题：</em><input type="text" name="lc_title" id="lc_title" required> <span style="color:#C39766;">*</span></div>                                <div class="clear"></div>                              </li>                              <li>                                <div class="main_ly_t1"><em>姓名：</em><input type="text" name="lc_name" id="lc_name" required><span style="color:#C39766;">*</span></div>                                <div class="clear"></div>                              </li>                              <li>                                <div class="main_ly_t1"><em>E-MAIL：</em><input type="text" name="lc_email" id="lc_email" required><span style="color:#C39766;">*</span></div>                                <div class="clear"></div>                              </li>                              <li>                                <div class="main_ly_t1"><em>联系电话：</em><input type="text" name="lc_tel" id="lc_tel" required><span style="color:#C39766;">*</span></div>                                <div class="clear"></div>                              </li>                                                            <li>                                <div class="main_ly_t1"><em>留言内容：</em><textarea name="lc_content" id="lc_content" required></textarea></div>                                <div class="clear"></div>                              </li>                              <li>                                <div class="yao">                                    <div class="main_ly_t2"><input type="submit" id="tijiao" value="提 交" onClick="return doSubmit();" style="background:#000; border-radius:5px;border:0;"></div>                                    <div class="main_ly_t3"><input type="reset" id="chongzhi" value="重 置" style="background:#000; border-radius:5px; border:0;"></div>                                </div>                              </li>                              <div class="clear"></div>                              </form>

<script type="text/javascript">function doSubmit(){    if (document.getElementById("lc_title").value==""){        alert("亲，请填写留言标题！");        document.getElementById("lc_title").focus();     //赋予焦点        return false;    }    if (document.getElementById("lc_name").value==""){        alert("亲，请填写您的姓名！");        document.getElementById("lc_name").focus();        return false;    }    if (document.getElementById("lc_email").value==""){        alert("亲，请填写电子邮件！");        document.getElementById("lc_email").focus();        return false;    }    if (!Isyx(document.getElementById("lc_email").value)){         alert("亲，请输入正确的电子邮件！");         document.getElementById("lc_email").focus();         return false;    }    if (document.getElementById("lc_tel").value==""){        alert("亲，请填写联系方式！");        document.getElementById("lc_tel").focus();        return false;    }    var reg =/(^0{0,1}1[3|4|5|6|7|8|9][0-9]{9}$)/;              //判断手机填写信息是否为正确手机号    if(!reg.test(document.getElementById("lc_tel").value)){         alert("亲，请输入正确的联系方式！");        document.getElementById("lc_tel").focus();        return false;     }    if (document.getElementById("lc_content").value==""){        alert("亲，请填写留言内容！");        document.etElementById("lc_content").focus();        return false;    }    return true;}</script>