NowJS throwing an error when trying to start nodejs server

im trying to start a node.js server with nowjs, but I get the following error:

    /var/www/vhosts/sitename.com/httpdocs/sitename/assets/js/node_modules/now.js:2
    TagName("head")[0].appendChild(fileref)}return nowObjects[uri]=now};window.now
                                                                        ^
    ReferenceError: window is not defined
        at /var/www/vhosts/sitename.com/httpdocs/sitename/assets/js/node_modules/now.js:2:9761
        at Object. (/var/www/vhosts/sitename.com/httpdocs/sitename/assets/js/node_modules/now.js:2:9794)
        at Module._compile (module.js:449:26)
        at Object.Module._extensions..js (module.js:467:10)
        at Module.load (module.js:356:32)
        at Function.Module._load (module.js:312:12)
        at Module.require (module.js:362:17)
        at require (module.js:378:17)
        at /var/www/vhosts/sitename.com/httpdocs/sitename/assets/js/app.js:35:14
        at Object. (/var/www/vhosts/sitename.com/httpdocs/sitename/assets/js/app.js:38:3)