解决JS表单验证只有第一个IF起作用的问题

if（条件语句）｛
 return false;
｝else{
 return true;
}
if（条件语句）｛
 return false;
｝else{
 return true;
}
if（条件语句）｛
 return false;
｝else{
 return true;
}

<script type="text/javascript">
 function checkForm() {
 var productName = true; 
 var chanDi = true;
 var muChanLiang = true;
 var zongChanLiang = true;
 var xiangQiang = true;
 var yuShouJia = true;
 var phone = true;
 var pattern = /^1[34578]\d{9}$/; //验证手机号正则表达式 
 if ($("#userName") == "") {
 alert("请输入产品名称!");
 /* alert($("#gsp_add_img_23").val()); */
 productName = false;
 } else if ($("#candi").val() == "") {
 alert("请输入产地!");
 chanDi = false;
 } else if ($("#muchan").val() == "") {
 alert("请输入亩产量!");
 muChanLiang = false;
 }else if ($("#zongChan").val() == "") {
 alert("请输入总产量!");
 zongChanLiang = false;
 } else if ($("#xiangqing").val() == "") {
 alert("请输入产品详情!");
 xiangQiang = false;
 } else if ($("#yushoujia").val() == "") {
 alert("请输入预售价!");
 yuShouJia = false;
 } else if (!pattern.test($("#userPhone").val())) {
 alert("手机号格式错误");
 phone = false;
 }
 if (productName == true && chanDi == true && muChanLiang == true && 
 zongChanLiang == true && xiangQiang == true && yuShouJia == true && phone == true) {
 $("#ListForm").submit();
 }
 } 
 </script>

<form action="$!webPath/new/fl_npsh.htm" method="post" name="ListForm"
 id="ListForm" enctype="multipart/form-data" >
 <!-- 类似首页楼层模块 -->
 <div style="width: 1020px; margin: 0 auto;">
 <div class="floor floor_purple"
 style="width: 1011px; border-top: 1px solid #eee;">
 <div class="liebiao"
 <!-- 给后台传一个id -->
 <input name="id" type="hidden" id="id" value="$!obj.id" />
 </div>
 <div class="liebiao">
 <!-- <span class="liebiao_left" style="color:red">*</span> -->
 <span class="liebiao_left">产品名称：</span> <input id="userName"
 type="text" name="product_name" class="shuruk"
 placeholder="例：灵宝SOD苹果(*必填项 *)" />
 </div>
 <div class="liebiao">
 <span class="liebiao_left">产品产地：</span> <input type="text"
 value="" name="product_origin" class="shuruk" id="candi"
 placeholder="例：灵宝寺河山(*必填项 *)" />
 </div>
 <div class="liebiao">
 <span class="liebiao_left">产品亩产量：</span> <input type="text"
 value="" name="mu_yield" class="shuruk" id="muchan"
 placeholder="例：每亩产量(*必填项 *)" />
 </div>
 <div class="liebiao">
 <span class="liebiao_left">产品总产量：</span> <input type="text"
 value="" name="sum_yield" class="shuruk"
 placeholder="例：总产量(*必填项 *)" id = 'zongChan'/>
 </div>
 <div class="liebiao" style="height: 60px;">
 <span class="liebiao_left"
 style="display: inline-block; height: 60px; line-height: 30px; float: left;">产品详情：</span>
 <textarea type="text" value="" id="xiangqing"
 name="product_details" class="shuruk02"
 placeholder="例：产品种植标准、产品优点、产品性能、储存注意事项等(*必填项 *)"></textarea>
 </div>
 <div class="liebiao">
 <span class="liebiao_left">产品预售参考价：</span> <input type="text"
 value="" id="yushoujia" name="advance_price" class="shuruk"
 placeholder="例：以每500g为单位(*必填项 *)" />
 </div>
 <div class="liebiao">
 <span class="liebiao_left">站主联系方式：</span> <input id="userPhone"
 value="" name="phone" class="shuruk" 
 placeholder="(*必填项 *)" />
 </div>
 <div class="liebiao" style="margin-top: 30px;">
 <input type="button" value="立即申请" class="tijiao" onclick="checkForm()">
 </div>
 </div>
 </div>
 </form>