nodejs write to existing file code example

Example 1: How to append to a file in Node?

// Asynchronously:
const fs = require('fs');

fs.appendFile('message.txt', 'data to append', function (err) {
  if (err) throw err;
  console.log('Saved!');
});

// Synchronously:
const fs = require('fs');

fs.appendFileSync('message.txt', 'data to append');

Example 2: data not write in file node js

const fs = require('fs');

fs.readFile('file.txt', 'utf-8', (err, data) => {
    if(err) {
        throw err;
    }
    console.log(data);
});