Javascript substr() optimized for Chinese Characters.

sub-ch-string

String.prototype.strLen = function() {
    var len = 0,
        offset;
    for (var i = 0, tmp = this.length; i < tmp; i++) {
        offset = (this.isCHS(i)) ? 2 : 1;
        len += offset;
    }
    return len;
};

String.prototype.strToChars = function(){
    var chars = [];
    for (var i = 0, tmp = this.length; i < tmp; i++){
        chars[i] = [this.substr(i, 1), this.isCHS(i)];
    }
    String.prototype.charsArray = chars;
    return chars;
};

String.prototype.isCHS = function(i){
    return (this.charCodeAt(i) > 255 || this.charCodeAt(i) < 0);
};

String.prototype.subCHString = function(start, end){
    var len = 0,
        str = '',
        offset;
    this.strToChars();
    for (var i = 0, tmp = this.length; i < tmp; i++) {
        offset = (this.charsArray[i][1]) ? 2 : 1;
        len += offset;

        if (end < len) {
            return str;
        } else if (start < len) {
            str += this.charsArray[i][0];
        }
    }
    return str;
};