How to find whether a particular string has unicode characters (esp. Double Byte characters)

Question

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

Answer 1

JavaScript holds text internally as UCS-2, which can encode a fairly extensive subset of Unicode.

But that's not really germane to your question. One solution might be to loop through the string and examine the character codes at each position:

function isDoubleByte(str) {
    for (var i = 0, n = str.length; i < n; i++) {
        if (str.charCodeAt( i ) > 255) { return true; }
    }
    return false;
}

This might not be as fast as you would like.