Read multiple files async

Question

I want to read multiple files simultaneously and apply the same function on data.

This code works correctly, but can someone please suggest any better way of writing this?

function fileread(path,stats,callback){
 var buffer = new Buffer(stats.size);
 fs.readFile(path, buffer, function(err, data){
 if(err){
 throw err;
 }
 callback(null, data);
 });
}
function testAsync() {
 var files = ['Statistics_Schema.json','seriesData'];
 async.map(files, fs.stat, function(err, stats){
 var i=0;
 async.map(files, function(path, callback){
 fileread(path, stats[i++], callback);
 },function(err, data){
 for(var j=0; j < data.length; j++){
 console.log(data[j].toString());
 }
 });
 });
}

• Junle Li: Use promise pattern. Recommend to read: strongloop.com/strongblog/…

Answer 1

I believe you can shorten it to just

function testAsync() {
 var files = ['Statistics_Schema.json', 'seriesData'];
 async.map(files, fs.readFile, function (err, data) {
 for(var i = 0, l = data.length ; i < l ; i++) {
 console.log( data[i].toString() );
 }
 });
}

Right now, you're first calling fs.stat on each file, only so you can create a buffer in your fileread method.

But fs.readFile does not take a buffer argument. It takes an options object (and there's no buffer option).

The Buffer object you're passing is an object, though, so Node doesn't complain. It just doesn't find any relevant fileRead options in that object either, so it's basically ignored.

So you don't need the buffer, which means you don't need fs.stat, which means you can skip almost all of your code.

Answer 2

Why not using fs.readFile? I just tested this code:

var async = require('async'),
 fs = require('fs'),
 files = ['file1.json', 'file2.json'];
async.map(files, fs.readFile, function(err, files) {
 if(err) {
 throw err;
 }
 files.forEach(console.log);
});

If you wanna be able to read the file contents then replace the last line with

files.forEach(function(file) {
 console.log(file.toString());
});

• konijn: He is using fs.readFile in fileread with a buffering option.
• Renato Gama: Hi @konjin - I thought that with both codes he would achieve the same results, then I googled about the difference in passing a buffer to readFileand could find nothing on the docs. Can you explain the difference?
• konijn: Interesting, it seems you are correct, passing buffer to readFile does not make any sense.
• konijn: Also, see this: codereview.stackexchange.com/a/59783/14625
• Renato Gama: At the time I answered @Flambino's answer wasn't visible to me, I believe its due to the migration from SO. Pretty much the same answer.