I'm using JavaScript to add append "✓" after a button's action comes back verified from the server. For the most part, it works OK, and I'm satisfied with how it looks. I haven't found an ASCII character to adequately communicat the same message.

My problem is that some older browsers, notably Firefox 3.6 and Camino do not understand this escape sequence, and so the user also sees "✓" instead of the checkmark character.

Is there a way to detect if the browser does not supprot this escape sequence and replace it with something else, e.g. "OK"? In other words, what goes in the if statement below?

// ...
var elemOK = document.createElement('span');
if ( ... ) { /* <----- what goes inside the if statement? */
    elemOK.innerHTML = '&check;'; // checkmark
} else {
    elemOK.innerHTML = 'OK';
}
elemActionButton.appendChild(elemOK);
// ....