Error occurs while Building Production 
parcel build index.html
� Build failed.
@parcel/namer-default: Target “main” declares an output file path of “index.js” which does not match the compiled bundle type “html”.
go to the jason file where it said main change it from “index.js” to “cool.js” save it then run the build again it should work. since i had the same problem
You should just remove the main attribute, delete the whole line. Then it should work!