<div class="form-group">
  <label for="modal_inputFile" class="col-md-3 control-label label-font">位置图:</label>
  <div class="col-md-9">
   <input type="text" readonly="" class="form-control" placeholder="点击选择文件">
   <input type="file" id="modal_inputFile">
   <img src="" class="img-responsive" id="modal-pre" alt="预览区" style="max-height: 300px">
  </div>
</div>

var file = document.getElementById(modal_inputFile'').files[0];
 if (!file) {
 return false;
 }
 var reader = new FileReader();
 reader.readAsDataURL(file);
 reader.onload = function(e) {
 var ib_pre = document.getElementById('modal-pre');
 ib_pre.src = this.result;
}

<img src="data:image/png;base64,iVBORXXXXXXXXXXXXX....XXXXXXX" class="img-responsive" id="modal-pre" alt="预览区" style="max-height: 300px">

//图片上传
$('#preUpload').on('click', function(e) {
 var data = new FormData();
 var _files = $("#modal_inputFile")[0].files[0];
 var ect = ($("#modal_inputFile")[0].files[0]).name.split('.')[1];
 if(ect !== 'png'){
  alert('请上传png图片!')
  return;
 }
 data.append("modal_file", _files);
 $.ajax({
  type: 'post',
  dataType: 'json',
  url: window.stnt_hosts + 'thirdAdmanage/upload/modal',
  data: data,
  contentType: false,
  processData: false
 }).done(function(data, status) {
  console.log('上传成功');
 }).fail(function(err) {
  console.log('上传失败');
 })
})

var formidable = require("formidable");
var form = new formidable.IncomingForm();
//临时目录
form.uploadDir = './upload/';
//预览图片上传
router.post('/upload/modal', function(req, res, next) {
 form.parse(req, function(err, fields, files) {
  if (files.modal_file) {
   rename(files.modal_file.path, files.modal_file.name, 'preview')
   res.send({
    stats:'success',
    data:[]
   })
  }
 })
});
function rename(old, _new, code, bId) {
 var path = './upload/' + code + '/';
  fs.exists(path, function(exists) {
   if (!exists) {
    fs.mkdir(path)
    console.log('创建文件夹！')
   }
   fs.renameSync(old, path + _new, function(err) {
    if (err) {
     console.log(err);
     return;
    }
    console.log('上传成功!')
   })
  })
}