Handle file uploads in node.js without express

upload.js

// call fileUploadRequestHandler( req, res ) from http.createServer callback context
// change ./files references to your files directory name

async function fileUploadRequestHandler( req, res )
{
  const fs = require(fs), path = require('path')
  
  // update the file name/ext here to a random or dynamic one (e.g supplied from querystring)
  const filename = 'example.txt'

  // update 10e6 for more/less than 10 MB post size
  const file_buffer = await getRequestInput( req, 10e6 )

  if ( ! file_buffer || ! file_buffer.length )
    return res.writeHead(400), res.end()
  
  // initiate uploads folder
  fs.existsSync('./files') || fs.mkdirSync('./files')

  try {
    await fs.writeFile(path.join('./files', filename), file_buffer, 'binary', err =>
    {
      if ( err ) throw new Error(err)
    })
  } catch (error) {
    console.log( '[ERROR] file upload ended with an error', error )    
    return res.writeHead(500), res.end()    
  }

  return res.end(filename)
}

function getRequestInput( request, limit )
{
  return new Promise(resolve =>
  {
    let body = Buffer.from('')
    
    request.on('data', data =>
    {
      body = Buffer.concat([ body, Buffer.from(data) ])
      body.length > limit && request.connection.destroy()
    })

    request.on('end', () => resolve(body))
  })
}

xhr.js

const input = document.querySelector('input[type=file]')
const file = input.files[0]
const xhr = new XMLHttpRequest

xhr.open('POST', 'http://your-server.co/files-handler', true)
xhr.setRequestHeader('Content-Type', 'application/octate-stream')
xhr.onreadystatechange = () =>
{
  if ( 4 == xhr.readyState ) {
    if ( 200 == xhr.status ) {
      console.log('uploaded to', xhr.responseText)
    } else {
      console.log('error uploading file')
    }
  }
}
xhr.send(file)