js检验文件格式

　HTML:

　　　<form id="uploadForm" method="post" class="layui-form">
   <div class="layui-form-item">
      <label class="layui-form-label">名称</label>
      <div class="layui-input-block">
         <input type="text" name="name" required lay-verify="required"
               placeholder="请输入文件名" autocomplete="off" class="layui-input">
      </div>
   </div>

   <div class="layui-form-item">
      <label class="layui-form-label">资料类型:</label>
      <div class="layui-input-block">
         <select name="datatypeid"  id="datatypeid"></select>
      </div>
      <input type="hidden" id="yincang">
   </div>
   <div class="layui-form-item">
      <label class="layui-form-label">上传文件</label>

      <div class="layui-input-block">
         <input class="layui-input" type="file" name="file" onchange="fileChange(this);"/>
      </div>
   </div>

   <div class="layui-form-item">
      <div class="layui-input-block">

         <input type="button" class="layui-btn" value="上传"
               onclick="upload()" />
      </div>
   </div>
</form>

Js 代码：

<script type="text/javascript">
    var isIE = /msie/i.test(navigator.userAgent) && !window.opera;
    function fileChange(target, id) {
        var fileSize = 0;
        var filetypes = [  ".xlsx", ".xls" ];//这里设置接受的文件类型
        var filepath = target.value;
        var filemaxsize = 1024 * 1;//接受的文件最大1M
        if (filepath) {
            var isnext = false;
            var fileend = filepath.substring(filepath.indexOf("."));
            if (filetypes && filetypes.length > 0) {
                for (var i = 0; i < filetypes.length; i++) {
                    if (filetypes[i] == fileend) {
                        isnext = true;
                        break;
                    }
                }
            }
            if (!isnext) {
                alertx("不接受此文件类型！");
                target.value = "";
                return false;
            }
        } else {
            return false;
        }
        if (isIE && !target.files) {
            var filePath = target.value;
            var fileSystem = new ActiveXObject("Scripting.FileSystemObject");
            if (!fileSystem.FileExists(filePath)) {
                alertx("附件不存在，请重新输入！");
                return false;
            }
            var file = fileSystem.GetFile(filePath);
            fileSize = file.Size;
        } else {
            fileSize = target.files[0].size;
        }

        var size = fileSize / 1024;
        if (size > filemaxsize) {
            alertx("附件大小不能大于" + filemaxsize / 1024 + "M！");
            target.value = "";
            return false;
        }
        if (size <= 0) {
            alertx("附件大小不能为0M！");
            target.value = "";
            return false;
        }
    }
</script>