I found this issue, when simply remove the containter with
docker rm. Seems there are something else still in my computer.
For example. I start a game from below command
docker run -d -p 8080:80 alexwhen/docker-2048
I play several times, and it records the highest score.
Then I delete the container and run it again, I found the highest score is not reset to zero.
So How to fully clean docker container?