react_app_build.sh

#assuming you are in your react app directory
mkdir /tmp/s3uploads
cp -ar build/static /tmp/s3uploads/
cd /tmp/s3uploads
#add gzip encoding to all the files
gzip -9 `find ./ -type f`
#remove .gz extension from compressed files
for i in `find ./ -type f`
do
   mv $i ${i%.*}
done
#sync your files to s3 static bucket and mention that these files are compressed with gzip encoding
#so that browser will not treat them as regular files
aws s3 --region $AWSREGION sync . s3://${S3_STATIC_BUCKET}/static/ --content-encoding gzip --delete --sse
cd -
rm -rf /tmp/s3uploads