How to stop a file from beign overwritten with fs.writefile

Question

The problem is that when I am trying to save data that I get from a chat room that is made with socket.io in nodejs, the file keeps getting overwritten once the user has submitted their message to the chatroom. However I want the user name + message to be added to the file instead of overwriting it, so both the username and the message will get stored in to the JSON file as a object.

This is what i tried at first:

socket.on('send-chat-message', message => {
socket.broadcast.emit('chat-message',{ message: message, name: users[socket.id] })
var collect = {
  message: message,
  name: users[socket.id] 
 }
  var savechatData = JSON.stringify(collect)
  fs.writeFile('./public/static/chattingdata/chat.json', savechatData, function (error) {
  if (error) {
  console.log("There has been an error saving your configuration data")
  console.log(error.message)
  return
  }
  console.log('Configuration saved succesfully')
  })
})
})

But that would just overwrite it. So then i tried like this:

socket.on('send-chat-message', message => {
socket.broadcast.emit('chat-message',{ message: message, name: users[socket.id] })
var collect = {
  message: message,
  name: users[socket.id] 
 }
  var savechatData = JSON.stringify(collect)
  fs.writeFile('./public/static/chattingdata/chat.json', {'flags': 'a'}, savechatData, function (error) {
  if (error) {
  console.log("There has been an error saving your configuration data")
  console.log(error.message)
  return
  }
  console.log('Configuration saved succesfully')
  })
})
})

But then i get the error: 'ERR_INVALID_OPT_VALUE_ENCODING'

So how could i fix this problem?

score 1 · Answer 1 · answered Apr 16 '21 at 12:59

1

fs.writeFile function's signature is fs.writeFile(file, data[, options], callback). The data parameter should be given as the second parameter and the optional options parameter as the third parameter. Refer Docs here

Change your code from

fs.writeFile('./public/static/chattingdata/chat.json', {'flags': 'a'}, savechatData, function (error){ // Callback })

to

fs.writeFile('./public/static/chattingdata/chat.json', savechatData, {'flags': 'a'}, function (error) { // callback })

answered Apr 16 '21 at 12:59

Kishore Sampath

973
6
13

This works but it still seems to overwrite the file. I have found that people said i have to use the flag a+ but this also overwrites the file. Which i dont want, because i want to add a new line to the file and not overwrite it. – SpringerJerry Apr 16 '21 at 13:18
1

@SpringerJerry Check this [solution](https://stackoverflow.com/questions/36093042/how-do-i-add-to-an-existing-json-file-in-node-js). They have asked to open the file first using `json.parse()`, then append the data to the file and lastly save the file again. – Kishore Sampath Apr 16 '21 at 13:40

How to stop a file from beign overwritten with fs.writefile

1 Answers1