Node.js get file extension

Im creating a file upload function in node.js with express 3.

I would like to grab the file extension of the image. so i can rename the file and then append the file extension to it.

app.post('/upload', function(req, res, next) {
    var is = fs.createReadStream(req.files.upload.path),
        fileType = >>>> I want to get the extension of the image here <<<<,
        os = fs.createWriteStream('public/images/users/' + req.session.adress + '.' + fileType);
});

How can i get the extension of the image in node.js?

I believe you can do the following to get the extension of a file name.

var path = require('path')

path.extname('index.html')
// returns
'.html'

I'm using this function to get a file extension, because I didn't find a way to do it in an easier way (but I think there is) :

function getExtension(filename) {
    var ext = path.extname(filename||'').split('.');
    return ext[ext.length - 1];
}

you must require 'path' to use it.

another method which does not use the path module :

function getExtension(filename) {
    var i = filename.lastIndexOf('.');
    return (i < 0) ? '' : filename.substr(i);
}


// you can send full url here
function getExtension(filename) {
    return filename.split('.').pop();
}

If you are using express please add the following line when configuring middleware (bodyParser)

app.use(express.bodyParser({ keepExtensions: true}));


var fileName = req.files.upload.name;

var arr = fileName.split('.');

var extension = arr[length-1];

It's a lot more efficient to use the substring() method instead of split() & pop()

Have a look at the performance differences here: http://jsperf.com/remove-first-character-from-string

// returns: 'html'
var path = require('path');
path.extname('index.html').substring(1);

path.extname will do the trick in most cases. However, it will include everything after the last ., including the query string and hash fragment of an http request:

var path = require('path')
var extname = path.extname('index.html?username=asdf')
// extname contains '.html?username=asdf'

In such instances, you'll want to try something like this:

var regex = /[#\\?]/g; // regex of illegal extension characters
var extname = path.extname('index.html?username=asdf');
var endOfExt = extname.search(regex);
if (endOfExt > -1) {
    extname = extname.substring(0, endOfExt);
}
// extname contains '.html'

Note that extensions with multiple periods (such as .tar.gz), will not work at all with path.extname.

A simple solution without need for require which solves the multiple period extension problem:

var filename = 'file.with.long.extension';
var ext = filename.substring(filename.indexOf('.')); 
//ext = '.with.long.extension'

Or if you don't want the leading dot:

var filename = 'file.with.long.extension';
var ext = filename.substring(filename.indexOf('.')+1); 
//ext = 'with.long.extension'

Make sure to test that the file has an extension too.

var Url = require('url');
var Path = require('path');
var path = 'http://i.imgur.com/Mvv4bx8.jpg?querystring=true';
var result = Path.extname(Url.parse(url).pathname); // '.jpg'