<p>To be more precise, I need to know whether (and if possible, how) I can find whether a given string has double byte characters or not. Basically, I need to open a pop-up to display a given text which can contain double byte characters, like Chinese or Japanese. In this case, we need to adjust the window size than it would be for English or ASCII.
Anyone has a clue?</p>

Why not let the window resize itself based on the runtime height/width?
Run something like this in your pop-up:
```
```
window.resizeTo(document.body.clientWidth, document.body.clientHeight);
```
```