<form class="layui-form forms" action="" method="post"  lay-filter="nei1s" id="nei1s">

<div class="layui-form-item">
    <label class="layui-form-label">分类</label>
    <div class="layui-input-block">
      <input type="checkbox" name="tag[]" title="写作" value="1">
      <input type="checkbox" name="tag[]" title="阅读" value="2">
      <input type="checkbox" name="tag[]" title="游戏" value="3">
    </div>
  </div>

</form>

<script>


var platform = '';                 //字符串形式
    var platform_arr = new Array();    //数组形式
    
    var obj = $("#nei1s").find('.layui-form-checked');
     
    obj.each(function () {
     	platform += $(this).prev().val() + ',';
     	platform_arr.push($(this).prev().val());
     });
     console.log(platform);
     console.log(platform_arr);	

</script>

简单高效，直接用