How to pass argument to custom command?

[colossatr0n]

I'm trying to call a codeblock function and pass an argument to it after mapping it to a command:

popup(word) -> {{
    alert(word)
}}

command show call popup(thePassedInArg)

which I'd like to call like this:

:show my-awesome-message

but I don't know how to reference an argument passed into a command, e.g., thePassedInArg.