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="$!webPath/new/fl_npsh.htm" method="post" name="ListForm"
  id="ListForm" enctype="multipart/form-data" >
  <!-- 类似首页楼层模块 -->
  <div style="width: 1020px; margin: 0 auto;">
  <div class="floor floor_purple"
   style="width: 1011px; border-: 1px solid #eee;">
   <div class="liebiao"
   <!-- 给后台传一个id -->
   <input name="id" type="hidden" id="id" value="$!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-: 30px;">
   <input type="button" value="立即申请" class="tijiao" onclick="checkForm()">
   </div>
  </div>
  </div>
 </form>