Change directory file upload nodejs

I'm using formidable to upload file with nodejs . I want change directory by type of file . I.e : img file to folder img , video to folder video ,.. Here is my code

 var form = new formidable.IncomingForm();
    var fileName = req.body.file;
    console.log(fileName); //log successfully file name 

if(fileName.match(/\.(jpg|jpeg|png)$/i)){
        form.uploadDir = path.join(__dirname, '../public/uploads/img');
    }else{
        form.uploadDir = path.join(__dirname, '../public/uploads');
    }
 form.on('file', function(field, file) {
    var d = new Date();
    var t = d.getTime();
    var newName = md5(file.name) + t;
    fs.rename(file.path,path.join(form.uploadDir,newName),function(err) {
        if(err)
            console.log(err);
        console.log('Success')
    });

});
   // log any errors that occur
    form.on('error', function(err) {
        console.log('An error has occured: \n' + err);
    });


    // parse the incoming request containing the form data
    form.parse(req, function(err, fields, files) {
    });

But I get error cannot read match of undefined in this line : if(fileName.match(/\.(jpg|jpeg|png)$/i)) . Where is my wrong ? Please help me

via Thanh Tùng