How to write a Node.js express API for file uploading?

In case somebody have the same issue, here is my full source code and explanation.

Background of my project

An ionic application which is using cordova-file-transfer plugin to upload file from photo library to a node.js express server.

My server code in app.js:

var express = require('express')
var multer = require('multer')
var bodyParser = require('body-parser')
var path = require('path')

var app = express()

// settings
app.set('views', path.join(__dirname,'views'))
app.set('view engine','jade')

// middleware
app.use(bodyParser.json())

// route
app.get('/', (req,res) => {
  res.render('index')
})

app.post('/', multer({dest:'./uploads/'}).single('upl'),(req,res) => {
  console.log(req.body)
  console.log(req.file)
  res.status(204).end()
})

// start
var server = app.listen(3000, () => {
  console.log('Started at port ' + server.address().port)
})

My client code upload():

upload() {

var options = new FileUploadOptions()
options.fileKey = "upl";              // this equal to <input type="file" id="upl">
options.fileName = 'test.jpg';
options.mimeType = "image/jpg";
options.chunkedMode = false;
options.params = {'directory' : 'uploads', 'fileName': 'test.jpg'};

var ft = new FileTransfer()
ft.upload(this.thumbnail, encodeURI('http://localhost:3000/'),
  (res) => {
    console.log("Code = " + res.responseCode)
    console.log("Response = " + res.response)
    console.log("Sent = " + res.bytesSent)
  },(error) => {
    alert("An error has occurred: Code = " + error.code);
    console.log("upload error source " + error.source);
    console.log("upload error target " + error.target);
  },options)
}

this.thumbnail is my file path, for example in my ios, the path is something like:

file:///Users/myusername/Library/Developer/CoreSimulator/Devices/81B513B7-AE34-4911-A9C9-57E293957BEC/data/Containers/Data/Application/C9A0BE15-EA4A-4DD8-9E75-BC960ECF50B7/tmp/cdv_photo_016.jpg