node fs append to 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: node js write file

// fs_write.js

const fs = require('fs');

// specify the path to the file, and create a buffer with characters we want to write
let path = 'ghetto_gospel.txt';
let buffer = new Buffer('Those who wish to follow me\nI welcome with my hands\nAnd the red sun sinks at last');

// open the file in writing mode, adding a callback function where we do the actual writing
fs.open(path, 'w', function(err, fd) {
    if (err) {
        throw 'could not open file: ' + err;
    }

    // write the contents of the buffer, from position 0 to the end, to the file descriptor returned in opening our file
    fs.write(fd, buffer, 0, buffer.length, null, function(err) {
        if (err) throw 'error writing file: ' + err;
        fs.close(fd, function() {
            console.log('wrote the file successfully');
        });
    });
});

Example 3: javascript fs read

fs.readFile('/etc/passwd', (err, data) => {
  if (err) throw err;
  console.log(data);
});

Example 4: writeFileSync

var fs = require('fs');

// Save the string "Hello world!" in a file called "hello.txt" in
// the directory "/tmp" using the default encoding (utf8).
// This operation will be completed in background and the callback
// will be called when it is either done or failed.
fs.writeFile('/tmp/hello.txt', 'Hello world!', function(err) {
  // If an error occurred, show it and return
  if(err) return console.error(err);
  // Successfully wrote to the file!
});

// Save binary data to a file called "binary.txt" in the current
// directory. Again, the operation will be completed in background.
var buffer = new Buffer([ 0x48, 0x65, 0x6c, 0x6c, 0x6f ]);
fs.writeFile('binary.txt', buffer, function(err) {
  // If an error occurred, show it and return
  if(err) return console.error(err);
  // Successfully wrote binary contents to the file!
});