How to read the content of files synchronously in Node.js?

Question

This is what I have:

#! /usr/bin/env node

var fs = require('fs'),
    files = fs.readdirSync(__dirname + '/files/'),

files.forEach(function(file) {
  fs.readFile(__dirname + '/files/' + file, 'utf8', function (error, data) {
    console.log(data)
  })
})

Even though I'm using readdirSync the output is still asynchronous:

alex@alex-K43U:~/node/readFiles$ node index.js 
foo 1

foo 3

foo 2

How to modify the code so the output becomes synchronous?

alex@alex-K43U:~/node/readFiles$ node index.js 
foo 1

foo 2

foo 3

I think your problem is that `forEach` doesn t garantee order, you should try with a dumb for loop. Also, you should use readFileSync if you want to read files syncronously — DrakaSAN, Dec 07 '15 at 14:15

score 65 · Accepted Answer · answered Dec 07 '15 at 14:03

You need to use readFileSync, your method is still reading the files asynchronously, which can result in printing the contents out of order depending on when the callback happens for each read.

var fs = require('fs'),
    files = fs.readdirSync(__dirname + '/files/');

files.forEach(function(file) {
  var contents = fs.readFileSync(__dirname + '/files/' + file, 'utf8');
  console.log(contents);
})

score 7 · Answer 2 · edited Jun 07 '18 at 12:39

7

That's because you read the file asynchronously. Try:

#! /usr/bin/env node

var fs = require('fs'),
    files = fs.readdirSync(__dirname + '/files/'),

files.forEach(function(file) {
  var data = fs.readFileSync(__dirname + '/files/' + file, 'utf8');
  console.log(data);
});

NodeJS Documentation for 'fs.readFileSync()'

edited Jun 07 '18 at 12:39

Justin Russo

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answered Dec 07 '15 at 14:02

Peter Paul Kiefer

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score 2 · Answer 3 · answered Dec 07 '15 at 14:02

2

Have you seen readFileSync? I think that could be your new friend.

answered Dec 07 '15 at 14:02

Daniel A. White

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How to read the content of files synchronously in Node.js?

3 Answers3

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