js判断文件类型大小并给出提示的实现方法

<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>

<script type="text/javascript"> var isIE = /msie/i.test(navigator.userAgent) && !window.opera; function fileChange(target, id) {  var fileSize = 0;  var filetypes = [ ".doc", ".docx" ];//这里设置接受的文件类型  var filepath = target.value;  var filemaxsize = 1024 * 10;//接受的文件最大10M   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) {   alert("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)) {   alert("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) {  alert("附件大小不能大于" + filemaxsize / 1024 + "M！");  target.value = "";  return false;  }  if (size <= 0) {  alert("附件大小不能为0M！");  target.value = "";  return false;  } } </script>