CODEWITHSUNDEEP
node.jsfs
Erel Segal-Halevi
Erel Segal-Halevi

Reputation: 36715

reading files asynchronously in parallel

My node.js application requires several files. I understand that it's recommended to read files asynchronously, so, apparently I have to do something like this:

fs.readFile("file1", function(...) {
  fs.readFile("file2", function(...) {
    fs.readFile("file3", function(...) {
       [my application]
    }
  }
}

However, in this case, the files will be read sequentially.

Is there a way to read many files in parallel, and still make sure that the application starts after ALL of them have been loaded?

Upvotes: 2

Views: 2802

Answers (3)

João Pimentel Ferreira
João Pimentel Ferreira

Reputation: 16233

You can also use the module async

const fs = require('fs')
const async = require('async')

async.each(
  ['dir1/file2.txt', 'dir2/file3.txt', 'dir/file5.txt'], 
  (file, callback) => {
    fs.readFile(file, (err, data) => {
      if (err) callback(Error(err))
      else {
        console.log(data)
        callback()
      }
    })
  },
  (err) => {
    if (err) {
      console.error(err)
    } else {
      console.log('All files have been read OK')
    }
})

Upvotes: 0

Finesse
Finesse

Reputation: 10801

You can use a modern Promise-based API:

import {promises as fs} from 'fs';

function readFiles(files) {
  return Promise.all(
    files.map(path => fs.readFile(path))
  );
}

readFiles(['file1', 'file2', 'file3'])
  .then(fileContents => {
    console.log('All the files are read', fileContents);
  });

Upvotes: 2

user123444555621
user123444555621

Reputation: 152956

Pretty easy.

var files = [...], remaining = files.length;
var callback = function () {
    remaining--;
    if (!remaining) {
        go();
    }
};
files.forEach(function(file) {
    fs.readFile(file, callback);
});

Upvotes: 3

Related Questions