How can I tell if a string contains multibyte characters in Javascript?

Question

Is it possible in Javascript to detect if a string contains multibyte characters? If so, is it possible to tell which ones?

The problem I\'m running into is this (ap

Answer 1

JavaScript strings are UCS-2 encoded but can represent Unicode code points outside the Basic Multilingual Pane (U+0000 - U+D7FF and U+E000 - U+FFFF) using two 16 bit numbers (a UTF-16 surrogate pair), the first of which must be in the range U+D800 - U+DFFF.

Based on this, it's easy to detect whether a string contains any characters that lie outside the Basic Multilingual Plane (which is what I think you're asking: you want to be able to identify whether a string contains any characters that lie outside the range of code points that JavaScript represents as a single character):

function containsSurrogatePair(str) {
    return /[\uD800-\uDFFF]/.test(str);
}

alert( containsSurrogatePair("foo") ); // false
alert( containsSurrogatePair("f