Rename files in all subdirectories.

rename.sh

# Finds all files in the current directory and subdirectories
# whose filenames match the expression "*.js" (ends with .js)
# then renames the files, changing their extension to ".ts".
# https://stackoverflow.com/questions/7450818/rename-all-files-in-directory-from-filename-h-to-filename-half
for file in $(find . -type f -name "*.js")
do
    mv "$file" "${file/.js/.ts}"
done