How can I get file extensions with JavaScript?

Question

See code:

var file1 = \"50.xsl\";
var file2 = \"30.doc\";
getFileExtension(file1); //returns xsl
getFileExtension(file2); //returns doc

function getFileExt         


        

Answer 1

There is a standard library function for this in the path module:

import path from 'path';

console.log(path.extname('abc.txt'));

Output:

.txt

So, if you only want the format:

path.extname('abc.txt').slice(1) // 'txt'

If there is no extension, then the function will return an empty string:

path.extname('abc') // ''

If you are using Node, then path is built-in. If you are targetting the browser, then Webpack will bundle a path implementation for you. If you are targetting the browser without Webpack, then you can include path-browserify manually.

There is no reason to do string splitting or regex.

Answer 2

var extension = fileName.substring(fileName.lastIndexOf('.')+1);

Answer 3

For most applications, a simple script such as

return /[^.]+$/.exec(filename);

would work just fine (as provided by Tom). However this is not fool proof. It does not work if the following file name is provided:

image.jpg?foo=bar

It may be a bit overkill but I would suggest using a url parser such as this one to avoid failure due to unpredictable filenames.

Using that particular function, you could get the file name like this:

var trueFileName = parse_url('image.jpg?foo=bar').file;

This will output "image.jpg" without the url vars. Then you are free to grab the file extension.

Answer 4

Fast and works correctly with paths

(filename.match(/[^\\\/]\.([^.\\\/]+)$/) || [null]).pop()

Some edge cases

/path/.htaccess => null
/dir.with.dot/file => null

Solutions using split are slow and solutions with lastIndexOf don't handle edge cases.

Answer 5

var file = "hello.txt";
var ext = (function(file, lio) { 
  return lio === -1 ? undefined : file.substring(lio+1); 
})(file, file.lastIndexOf("."));

// hello.txt -> txt
// hello.dolly.txt -> txt
// hello -> undefined
// .hello -> hello

Answer 6

Wallacer's answer is nice, but one more checking is needed.

If file has no extension, it will use filename as extension which is not good.

Try this one:

return ( filename.indexOf('.') > 0 ) ? filename.split('.').pop().toLowerCase() : 'undefined';