Synchronously append data to a file, creating the file if it does not yet exist. data can be a string or a Buffer.

The mode option only affects the newly created file. See open for more details.

import { appendFileSync } from 'node:fs';

try {
  appendFileSync('message.txt', 'data to append');
  console.log('The "data to append" was appended to file!');
} catch (err) {
  // Handle the error
}

If options is a string, then it specifies the encoding:

import { appendFileSync } from 'node:fs';

appendFileSync('message.txt', 'data to append', 'utf8');

The path may be specified as a numeric file descriptor that has been opened for appending (using fs.open() or fs.openSync()). The file descriptor will not be closed automatically.

import { openSync, closeSync, appendFileSync } from 'node:fs';

let fd;

try {
  fd = openSync('message.txt', 'a');
  appendFileSync(fd, 'data to append', 'utf8');
} catch (err) {
  // Handle the error
} finally {
  if (fd !== undefined)
    closeSync(fd);
}