There is cloud server saving, but Unity + Browser games don't always behave nicely together. There are a few "proper" ways to exit the game to ensure the save goes through to the server:
1) Use the "force save" button in the settings menu. This will work 100% of the time.
2) Rather than clicking the "X" in your browser window or tab to close the game, use the "ESC" key and use the in-game prompt to exit the game. This will also force the save logic to run.
Sorry for the inconvenience!
Under rating threshold (hideshow)
Tower Defense and idling is match made in hell. money isn't problem instead problem is energy and that is needed on n+1 things more and more ("luckily" heroes can be upgraded witgh gold instead energy) so long journey ahead.