function literalTuple < T extends string , U extends [ T , ... T [ ] ] > ( ... args ) { return args ; } const modern = literalTuple ( "last 1 Chrome version" , "last 1 Safari version" , "last 1 Edge version" , "last 1 Firefox version" , "Firefox ESR" ) ; const ie11 = literalTuple ( "IE 11" ) ; const all = literalTuple ( ... modern , ... ie11 ) ; const config = { all , ie11 , modern , production : all } ; module . exports = config ;