Deno shell (REPL)

The Deno REPL (Read Eval Print Loop) is a dedicated Deno command shell that can help you to experiment and learn without having to save and run program files.

You can enter deno repl or simply deno in your terminal. Exit the shell by entering close() or pressing Ctrl-D to terminate the session.

Here’s an example of a session.

$ deno
Deno 1.12.2
exit using ctrl+d or close()
> "Hello"
> 1
> 1 + 1
> 1 + 1 * 2
> console.log("Hello")

The shell always prints out the value of the expression you enter.

In the last case (before the final prompt), evaluating the expression console.log("Hello") causes Hello to be printed as a side effect; since the expression itself doesn’t return any value, however, the shell prints undefined.