How to Write a File Using Writefile or Writefilesync in Node-Js

In Node.js, resource intensive operations such as I/O are performed asynchronously, but have a synchronous counterpart (e.g. there exists a fs.readFile and its counterpart is fs.readFileSync). Since Node is single-threaded, you should be careful when using synchronous operations, because they will block the entire process. Here we are going to see how to write a file using writefile or writefilesync in node.js

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!
});

fs.writeFileSync behaves similarly to fs.writeFile, but does not take a callback as it completes synchronously and therefore blocks the main thread. Most node.js developers prefer the asynchronous variants which will cause virtually no delay in the program execution.

Note: Blocking the main thread is bad practice in node.js. Synchronous function should only be used when debugging or when no other options are available.