socket.js

//server
io.on('connection', socket => {
  //read and send file
  ......
  //update and send data
  socket.on('updateFile', data => {
    //update your file
    ...
    //send new on client
    socket.emit('updateData', data)
  })
})

//client

socket.emit('updateFile', data)
socket.on('updateData', data => console.log(data))