<div class="form-group">
  <label>File input</label>
  <input type="file" name="file" id="file">
  <p id="result"></p>
  <img id="img" src="">
</div>
<button id="upload" class="btn btn-default">提交</button>

function uploadFile(){
 var file = document.getElementById("file")
 var formData = new FormData();
 formData.append('file',file.files[0]);
 $.ajax({
  url: '/upload',
  type: 'POST',
  data: formData,
  // async: false,
  cache: false,
  contentType: false,
  processData: false,
  success: function(data){
   if(200 === data.code) {
    $('#result').html("上传成功！");
    $('#img').attr('src',data.data);
   } else {
    $('#result').html("上传失败！");
   }
   console.log('imgUploader upload success');
  },
  error: function(){
   $("#result").html("与服务器通信发生错误");
  }
 });
}

function postPage() {
    var uploada = document.getElementById('upload');
    uploada.addEventListener("click",function () {
      uploadFile();
    },false);
}

window.onload = function () {
  postPage();
}

var storage = multer.diskStorage({
  destination: function (req, file, cb){
    cb(null, './public/images')
  },
  filename: function (req, file, cb){
    cb(null, file.originalname)
  }
});
var upload = multer({
  storage: storage
});
router.post('/upload', upload.single('file'), function (req, res, next) {
  var url = 'http://' + req.headers.host + '/images/' + req.file.originalname
  res.json({
    code : 200,
    data : url
  })
});

upload.single(‘file'), //适用于单文件上传。
upload.array(‘file',num), //适用于多文件上传，num为最多上传个数，上传文件的数量可以小于num。