Changes to CSS and JavaScript applies only after deploying static content

For now you only have this way to apply changes. Magento should be apply changes to pub/static dir but it not. This still know bug. Hope it should be fix soon
You can apply new changes by command as like you do. This way will take some times but should work
My way when i modify js from my extension . I just go to pub dir and clear folder

\pub\static\frontend\Magento\luma\en_US\<Vendor_Module>\js

You can do same with css files when customize styles

Magento have different strategy to materialize static assets.Copy and Link. When you run setup:static-content:deploy this command use Copy strategy and file will be materialized in static folder and will not not change when you change original.

If you cleanup static folder and open page in browser Link strategy will be used and link on original file created. So you will modify source and see changes