Random Thoughts

Don’t want to use JavaScript? What about Tcl? Or LOLCODE?

Wouldn’t it be neat if web browsers had more client-side languages available? Wouldn’t it be kind of cool if you could code up your app in Tcl and place it in a script tag? Well, it turns out you actually can (sort of)! The below Tcl code is mostly non-sense, but it does do some DOM manipulation, and you can see it in action here. 

<script type="text/tcl">

proc appendTextNodeToElement {divId text} {
    set div [document getElementById $divId]
    set textNode [document createTextNode $text]
    $div appendChild $textNode
}

proc listNames {name1 name2} {
    if {== $name1 $name2} {
        set nameStr $name1
    } else {
        set nameStr "$name1 and $name2"
    }
    puts "hi $nameStr"
    return $nameStr
}

appendTextNodeToElement "testDiv1" "This is a test!"
set names [listNames "Bob" "Alice"]
appendTextNodeToElement "testDiv2" $names
appendTextNodeToElement "testDiv3" "2 + 2 = [+ 2 2]"

</script>

It turns out that when a web browser is parsing a script tag, if it doesn’t recognize the “type” attribute, it will ignore the code within the tag. This allows newer browsers to support additional languages without breaking older browsers. However, the older browsers still leave the contents between its opening and closing tags there, so if you have some JavaScript code that will parse and interpreted it, you can execute it.

The idea fascinated me and I wanted to see if I could whip up a proof of concept. I found a neat open source Tcl interpreter written in C called Picol, which was only 550 lines and covered only a sub-set of the language. I figured this was perfect for my needs and decided to see if I could port it to JavaScript. The port was really straight forward and I was pretty amazed when I actually saw it working. I went ahead and added in a few DOM manipulation functions, but decided not to get too carried away. The code for this is available here. I only went far enough to get a proof of concept though, so it’s not very feature rich. I also don’t really have any plans to go further with this, I just sort of got excited at the idea and wanted to see what would happen.

I also decided to search around and see anyone else had ported other languages for use on the client side. I ended up finding some code written by a Dutch programmer which allows for LOLCODE in the browser (zip mirrored here). However, rather than interpreting the code, his method converts the LOLCODE to JavaScript, and then appends this new JavaScript into the web page via a script tag. Still neat though.

Also, I’m aware interpreting code with an interpreted language isn’t the best idea performance wise, and that there is currently a growing number of languages that compile into JavaScript. So client-side developers aren’t technically limited to just JavaScript, but I do still find the idea of JavaScript-based interpreters kind of neat.

Lastly, there are a couple of JavaScript Tcl interpreters out there already. I played around with a few, but ultimately found them a little too confusing, and I wasn’t sure they were made for what I wanted to do (basically act as a JavaScript substitute), so I passed them over when doing this experiment. However, I’ll link to them below for those of you who are curious.