Laravel Mix created js files in wrong directory (Laravel 5.4)

I store my assets in /storage/app/public/(css/js/img) But if I compile my js for example in /storage/app/public/js it is published in /storage/app//js what is the problem here??

mix.js('resources/assets/js/app.js', '../storage/app/public/js/app.js');->Works but file is published there ->/storage/app//js

mix.js('resources/assets/js/app.js', 'storage/app/public/js/app.js'); ->Doesn't work .... Error below

...
 94% asset optimization
 95% emittingError: EEXIST: file already exists, mkdir '/Users/janweskamp/PhpstormProjects/laravel-test/public/storage'

npm ERR! Darwin 16.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/lib/node_modules/npm/bin/npm-cli.js" "run" "dev"
npm ERR! node v7.6.0
npm ERR! npm  v4.1.2
npm ERR! code ELIFECYCLE
npm ERR! @ dev: `node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @ dev script 'node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the  package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js
npm ERR! You can get information on how to open an issue for this project with:
npm ERR!     npm bugs 
npm ERR! Or if that isn't available, you can get their info via:
npm ERR!     npm owner ls 
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/janweskamp/PhpstormProjects/laravel-test/npm-debug.log