I played a lot of io games like Agar.io , Slither.io , and Deeep.io. I started seeing io games where the creator claimed they created it for example, Blocktanks.io

I wanted to know if there is some sort of program or website you use to create one. If there aren't any programs or websites like so, then I would like to know how you would do to it for scratch as a last resort.