Hi.
Dynamic text fields created by the Text Tool (T) are canvas based texts. And characters in canvas texts can't be styled individually.
The easiest solution will be to use a Label component (Window > Components (Ctrl/Cmd + F7)) which renders DOM labels. In this way, you could, for example, style your text like this:
setTimeout(function() // the timeout is needed to access components when the code is iniatialized
{
var labelInstance = document.getElementById("yourTextID");
labelInstance.innerHTML = "This is a <strong>strong</strong> word and this is an <i>italic<i/> word.";
}, 0);
I hope this helps.
Regards,
JC