No callback file operations

Sep 19, 2017

Reading and writing files in JS tends to get messy. But not anymore, with Node 8, async / await support combined with Util.promisify we can read and write to a file without a single callback or “then”. Enough talk, actual code ---

use strict';

const FS   = require('fs');
const Util = require('util');

const updateFile = async (filename = 'fun.xml') => {
  const readFile = Util.promisify(FS.readFile); // promisify readFile so it works with await
  const fileContents = await readFile(`${__dirname}/xml/${filename}`);
  console.log('Current file contents - ', fileContents.toString());

  const writeFile = Util.promisify(FS.writeFile); // promisify writeFile so it works with await
  await writeFile(`${__dirname}/xml/${filename}`, fileContents.toString().replace(/foo/, 'bar'));
  console.log('File updated!');
};

updateFile();

Now we can just run this simply by -

$ node file_fun.js

That’s it, we read and wrote to a file in JS without any ugly callbacks, “thens” or libraries.