Post data in local file without replacing existing data

Question

Here is my code which will get data from the postman and write to a file but while writing it replacing the existing data how to fix that in this code.

app.post('/postUser', function (req, res) {
    req.on('data', function (data) {
        console.log(data.toString());

        fs.writeFile('test.json', data, function (err) {
            if (!err) {
                console.log("Finished writing")
            }
        });
    });
});

My output should be like this.

[
  {
    "name":"Alpha",
    "password":"123",
    "id": 1
  },
  {
    "name":"beta",
    "password":"123",
    "id": 2
  }
]

When I use appendFile I am getting output like this :

[
    {
        "name": "alpha",
        "password": "123",
        "id": 4
    }
]  {
        "name": "sdad",
        "password": "123",
        "id": 4
    }

Potential duplicate: https://stackoverflow.com/questions/3459476/how-to-append-to-a-file-in-node#11267583 — wmash, Oct 19 '18 at 10:58
I need output like i mentioned this like shows to append if i use append it printing the data like this [ { "name":"Alpha", "password":"123", "id": 1 } ] { "name":"beta", "password":"123", "id": 2 } — Dark Ninja, Oct 19 '18 at 11:01

wmash · Accepted Answer · 2018-10-19T13:24:55.677

0

app.post("/postUser", function(req, res) {
    req.on("data", function(data) {
        var newData;

        fs.readFile("test.json", function(readErr, fileData) {
            if (readErr) {
                console.error(readErr);
            }
            newData = JSON.parse(fileData).push(data);

            fs.writeFile("test.json", newData, function(writeErr) { 
                if (writeErr) {
                    console.error(writeErr);
                }
                console.log("Finished writing!");
            });
        });
    });
});

The way I usually get around this problem is to read the existing data and then append (push) your new data to the existing and write the result

edited Oct 19 '18 at 13:24

answered Oct 19 '18 at 10:56

wmash

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How to do this with post method – Dark Ninja Oct 19 '18 at 12:44
TypeError: fileData.push is not a function getting this error – Dark Ninja Oct 19 '18 at 13:20
You most likely need to parse the result using `JSON.parse()`. I will update my answer. What is the value of `fileData` before you mutate it? – wmash Oct 19 '18 at 13:23
[ { "name":"Alpha", "password":"123", "id": 1 }] – Dark Ninja Oct 19 '18 at 13:29
I need this to be completed can you help me in private – Dark Ninja Oct 19 '18 at 13:31
If you use the `JSON.parse()` function I have mentioned in my answer, it should work – wmash Oct 19 '18 at 13:40
Yea i used now in my json file its printing 2 instead of data – Dark Ninja Oct 19 '18 at 13:44
Brilliant :) so is that fixed now? – wmash Oct 19 '18 at 13:45
But i need data bro as i mentioned in the question above – Dark Ninja Oct 19 '18 at 13:47
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/182148/discussion-between-wmash-and-dark-ninja). – wmash Oct 19 '18 at 13:47
check the chat dood – Dark Ninja Oct 19 '18 at 13:56

score 0 · Answer 2 · answered Oct 19 '18 at 11:04

The writeFile method will just replace the data if any present in the file or will create a file if not exists and write data to it.

Instead of fs.writFile use the appendFile method to append any data to the file.

app.post('/postUser', function (req, res) {
    req.on('data', function (data) {
        console.log(data.toString());

        fs.appendFile('test.json', data, function (err) {
            if (!err) {
                console.log("Finished writing")
            }
        });
    });
});

But see my output in my question for the append file i am getting data outside the array — Dark Ninja, Oct 19 '18 at 11:50

Atishay Jain · Answer 3 · 2018-10-19T11:21:06.680

First read the file and append it with your changes and write it again.

app.post('/postUser', function (req, res) {
    req.on('data', function (data) {
        fs.readFile('test.json', 'utf8', function(err, file){
            //handle error
            if(!file) {
                var file = '';
            }
            var temp = JSON.parse(file);
            temp.push(data);    
            fs.writeFile('test.json', temp, function (err) {
                //handle error
                console.log("FILE STORED")
            });
        })
    });
});

Post data in local file without replacing existing data

3 Answers3