How to append new row in exist csv file in nodejs json2csv?

Use csv-write-stream function to append data in csv file.

https://www.npmjs.com/package/csv-write-stream Add this line,with flag "a"

writer.pipe(fs.createWriteStream('out.csv', {flags: 'a'}))

Seems, latest version of json2csv has dedicated method called .parse() to convert JSON to CSV compatible string. I tried json2csv.parse() converter and it works for me.

Common Issue:

I found a common issue in the solutions given here. The solutions don't append data without HEADER if we run the method multiple times.

Solution:

I used the header boolean option provided by json2csv to fix the issue. If we parse with {header:false} option we will get data as rows.

// Rows without headers.
rows = json2csv(data, { header: false });

Below is the code that works exactly I mentioned above:

Example Code:

Below is the code sample:

const fs = require('fs');
const path = require('path');
const json2csv = require('json2csv').parse;
const write = async (fileName, fields, data) => {
    // output file in the same folder
    const filename = path.join(__dirname, 'CSV', `${fileName}`);
    let rows;
    // If file doesn't exist, we will create new file and add rows with headers.    
    if (!fs.existsSync(filename)) {
        rows = json2csv(data, { header: true });
    } else {
        // Rows without headers.
        rows = json2csv(data, { header: false });
    }

    // Append file function can create new file too.
    fs.appendFileSync(filename, rows);
    // Always add new line if file already exists.
    fs.appendFileSync(filename, "\r\n");
}

Calling Write Function

We have 3 parameters:

fields = ['Name', 'Position', 'Salary'];
    data = [{
        'Name': 'Test1',
        'Position': 'Manager',
        'Salary': '$10500'
    },
    {
        'Name': 'Test2',
        'Position': 'Tester',
        'Salary': '$5500'
    }, {
        'Name': 'Test3',
        'Position': 'Developer',
        'Salary': '$5500'
    }, {
        'Name': 'Test4',
        'Position': 'Team Lead',
        'Salary': '$7500'
    }];

Now calling the function write:

write('test.csv', fields, data);

Every time we call above method, it writes from a new line. It writes headers only once if file doesn't exist.

The following code will do what you asked:

1. When run the first time- will write the headers
2. Each run after that - will append json the data to the csv file

var fs = require('fs');
var json2csv = require('json2csv');
var newLine = '\r\n';

var fields = ['Total', 'Name'];

var appendThis = [
  {
    Total: '100',
    Name: 'myName1',
  },
  {
    Total: '200',
    Name: 'myName2',
  },
];

var toCsv = {
  data: appendThis,
  fields: fields,
  header: false,
};

fs.stat('file.csv', function (err, stat) {
  if (err == null) {
    console.log('File exists');

    //write the actual data and end with newline
    var csv = json2csv(toCsv) + newLine;

    fs.appendFile('file.csv', csv, function (err) {
      if (err) throw err;
      console.log('The "data to append" was appended to file!');
    });
  } else {
    //write the headers and newline
    console.log('New file, just writing headers');
    fields = fields + newLine;

    fs.writeFile('file.csv', fields, function (err) {
      if (err) throw err;
      console.log('file saved');
    });
  }
});