internationalization - Turkish case conversion in JavaScript

Question

I want to convert strings to lower or upper case in JavaScript in the locale I wanted. I think standard functions like toUpperCase() and toLocaleUpperCase() do not satisfy this need. toLocale functions do not behave as they should.

For example, in Safari 4, Chrome 4 Beta, Firefox 3.5.x on my system it converts strings with Turkish characters incorrectly. The browsers respond to navigator.language as "en-US", "tr", "en-US" respectively. But there is no way to get user's Accept-Lang setting in the browser as far as I could found. Only Chrome gives me "tr" although I have configured every browser Turkish locale preferred. I think these settings only affect HTTP header, but we can't access to these settings via JavaScript.

In the Mozilla documentation it says

The characters within a string are converted to ... while respecting the current locale. For most languages, this will return the same as ...

I think it's valid for Turkish, it doesn't differ it's configured as en or tr. In Turkish it should convert "D?N?" to "din?" and "DIN?" to "d?n?" or vice-versa.

Is there any JavaScript library that satisfies this need? I think it should not only converting correctly in user's locale, but also it should support conversion via a locale parameter. Because developers cannot access to user's configured preferred language.

Answer 1

Coming back to this years later to provide more up to date solution.

There is no need for the hack below,

just use String.toLocaleUpperCase() and String.toLocaleLowerCase()

"din?".toLocaleUpperCase('tr-TR') // "D?N?"

All modern browsers support this now.

---

[ OLD, DO NOT USE THIS ]

Try these functions

String.prototype.turkishToUpper = function(){
    var string = this;
    var letters = { "i": "?", "?": "?", "?": "?", "ü": "ü", "?": "?", "?": "?", "?": "I" };
    string = string.replace(/(([i???ü??]))+/g, function(letter){ return letters[letter]; })
    return string.toUpperCase();
}

String.prototype.turkishToLower = function(){
    var string = this;
    var letters = { "?": "i", "I": "?", "?": "?", "?": "?", "ü": "ü", "?": "?", "?": "?" };
    string = string.replace(/(([?I??ü??]))+/g, function(letter){ return letters[letter]; })
    return string.toLowerCase();
}

// Example
"D?N?".turkishToLower(); // => din?
"DIN?".turkishToLower(); // => d?n?

I hope they will work for you.