NodeJS concatenate all files in a directory

Question

Is there a faster or more succinct way to concatenate all of the files located in a directory using NodeJS?

In bash I could do something like this:

for file in $1
do
  cat "$file"
  echo
done > $2;

Here is what I'm doing now:

var fs = require('fs');
var Promise = require('bluebird');

module.exports = function(directory, destination) {
    return new Promise((resolve, reject) => {
        fs.readdir(directory, (err, files) => {
            if (err) {
                return reject(err);
            }

            (function next() {
                var file = files.shift();
                if (!file) {
                    return resolve();
                }

                fs.readFile(directory + '/' + file, (err, content) => {
                    if (err) {
                        return reject(err);
                    }

                    fs.appendFile(destination, '\n' + content, (err) => {
                        if (err) {
                            return reject(err);
                        }

                        return next();
                    });
                });
            })();
        });
    });
};

Answer 1

That ?

require('child_process').execSync('cat *').toString('UTF-8')

:D

Answer 2

If you're going to use bluebird than you get the benefit of promisification. You can use promisifyAll() to convert all error first callback accepting async functions in the fs module to return a promise. You can read more about in the above promisification link.

The below code reads in all of the files as strings and then reduces all of their contents into a single string and writes that string to the destination.

Its probably best to not catch() any returned errors here. Rather, the caller should attach a catch() to handle any returned errors as they need.

const Promise = require('bluebird')
const fs = Promise.promisifyAll(require('fs'))
const path = require('path')

module.exports = (directory, destination) => {
  return fs.readdirAsync(directory)
    .map(file => fs.readFileAsync(path.join(directory, file), 'utf8'))
    .then(contents => fs.writeFileAsync(destination, contents.join('\n')))
}

Answer 3

Using the async library you can easily read files in parallel and then join the results.

const fs = require("fs");
const async = require("async");
const path = require("path");

module.exports = function(directory, destination) {

  return new Promise((resolve, reject) => {

    fs.readdir(directory, (err, files) => {
        if (err)
            return reject(err);

        files = files.map(file => path.join(directory,file));

        //Read all files in parallel
        async.map(files, fs.readFile, (err, results) => {
            if (err)
                return reject(err);

           //results[0] contents of file #1
           //results[1] contents of file #2
           //results[n] ...

            //Write the joined results to destination
            fs.writeFile(destination, results.join("\n"), (err) => {
                if (err)
                    return reject(err);

                resolve();
            });
        });

    });
  });
}