He was also comparing to CoffeeScript, and sadly there's no way to do it there. This is the one feature that keeps me from using CoffeeScript, the lack of REPL integration--I have no idea how other people do without MozRepl or SwankJS or something homegrown. If I don't have something akin to Slime for emacs, it really frustrates me. I assume I'm not that smart or extra lazy.
I question your use of "only" able to use your own editor. There are myriad problems with using Firebug to write your code in: It doesn't save your code so if the browser crashes or hangs (which happens all too much with my installation of Firefox) you lose it; if Firebug starts behaving wonky (again, happens all the time) you lose it; you have to copy and paste the code into your editor once it's done; and, the editing mode itself is awful, of course. This is, as opposed to, say, MozRepl, which is instead convenient and safe. I assume the ClojureScript environment is as nice or nicer.
I question your use of "only" able to use your own editor. There are myriad problems with using Firebug to write your code in: It doesn't save your code so if the browser crashes or hangs (which happens all too much with my installation of Firefox) you lose it; if Firebug starts behaving wonky (again, happens all the time) you lose it; you have to copy and paste the code into your editor once it's done; and, the editing mode itself is awful, of course. This is, as opposed to, say, MozRepl, which is instead convenient and safe. I assume the ClojureScript environment is as nice or nicer.