最新版はこちら http://code.google.com/p/kanaxs/ ひらがな⇒カタカナ String.prototype.toKatakanaCase = function() { var i, c, a = []; for(i=this.length-1;0<=i;i--) { c = this.charCodeAt(i); a[i] = (0x3041 <= c && c <= 0x3096) ? c + 0x0060 : c; }; return String.fromCharCode.apply(null, a); }; "ぁぃぅぇぉあいうえお".toKatakanaCase(); // ァィゥェォアイウエオ カタカナ⇒ひらがな String.prototype.toHirakanaCase = function() { var i, c, a = []; for(i