Are there any shortcut keys by which I can work faster?
It appears that repl.it uses the open-source readline, which happens to use most of the default key bindings in emacs. The readline bindings can be found in https://en.wikipedia.org/wiki/GNU_Readline#Emacs_keyboard_shortcuts
There a few. To run while you're in the editor you can do command(mac)/control(win/linux) + enter.
There are also a lot of shortcuts in the editor. If you right-click in it it will show the commands and will have a shortcut next to each thing it can do.