In your after/syntax/javascript.vim: syntax match javascriptReturnError /return\s*\n\r\?\s*\w.*$/ ... highlight link javascriptReturnError Error

In your after/syntax/javascript.vim: syntax match javascriptReturnError /return\s*\n\r\?\s*\w.*$/ ... highlight link javascriptReturnError Error Obviously you can play around with the regex to tweak what matches.