So basically, I need advice how to write javascript function withouth breaking the Quest.

The function needs to be able to flash one character for X amount of time and then another character for X amount of time.

I looked into playercore.js and I tracked how unscrambleTX and typerwiterTX works so I could try to do it myself but I know I could easily break the whole thing so I would rather ask for advice here.

So I to make my question more clear I will use code, also I have misspelled the names of the functions.
FXtypewriter istead of TX

So here is what I am trying to achieve in a gif : http://dwarffortresswiki.org/images/7/74/Icons.gif

As you see there are two characters flashing in one space.

Now here is what I have created in the playercore.js

    };
		$.fn.flashcharacter = function (speed) {
        this.each(function () {
            var $ele = $(this), str = $ele.text(), progress = 0;
            $ele.text('');
            var timer = setInterval(function () {
                $ele.text(str.substring(0, progress++) + ((progress & 1) && progress < str.length ? '_' : ''));
                if (progress >= str.length) setInterval(timer);
            }, speed);

Now the thing is, this is just copypasted from the fn.typewriter because I have NO idea what to change to make it flash two characters after X amount of time. Am I still too vague for anybody to help me with this?

EDIT: I also should mention that this references many other parts within the playercore.js so this sole section won´t probably explain it very well...

EDIT!!: I realized this is all a mistake because I cannot edit the playercore.js, simply because it would make it unplayable for anybody else who tries to downloand my game.

Add this to playercore.js (I added it to an attribute, and then output that inside script tags):

       flashers = [];
       flag = false;
       setInterval(function() {
         for (i = 0; i < flashers.length; i++) { 
           $(flashers[i]).css('color', flag ? 'black' : 'white');
         }
         flag = !flag;
      }, 200);
     
     
      function startFlash(elementId) {
        flashers.push (elementId);
      }

      function stopFlash(elementId) {
        index = flashers.indexOf(elementId);
        $(elementId).css('color', 'black');
        if (index > -1) {
          flashers.splice(index, 1);
        }
      }

You can then do this to start an element with the id "blink" flash:

JS.startFlash ("#blink")

And this to stop it:

JS.stopFlash ("#blink")

Wow, thanks! I will use it and try to disassemble it on my own to expand my knowledge.