Node.js get file extension

// 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}));

It's a lot more efficient to use the substr() 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').substr(1);

Update August 2019 As pointed out by @xentek in the comments; substr() is now considered a legacy function (MDN documentation). You can use substring() instead. The difference between substr() and substring() is that the second argument of substr() is the maximum length to return while the second argument of substring() is the index to stop at (without including that character). Also, substr() accepts negative start positions to be used as an offset from the end of the string while substring() does not.

Update

Since the original answer, extname() has been added to the path module, see Snowfish answer

Original answer:

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);
}

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'

If you would like to get all extensions in a file name (e.g. filename.css.gz => css.gz), try this:

const ext = 'filename.css.gz'
  .split('.')
  .filter(Boolean) // removes empty extensions (e.g. `filename...txt`)
  .slice(1)
  .join('.')

console.log(ext) // prints 'css.gz'