Regex number generator

//Credit: Bart Kiers 2011
function regex_range(from, to){
        if(from < 0 || to < 0) {
            //throw new Exception("Negative values not supported"); 
            return null;
        }
        if(from > to) {
            //throw new Exception("Invalid range from..to, from > to"); 
            return null;
        }

        var ranges = [];
        ranges.push(from);
        var increment = 1;
        var next = from;
        var higher = true;

        while(true){
            next += increment;
            if(next + increment > to) {
                if(next <= to) {
                    ranges.push(next);
                }
                increment /= 10;
                higher = false;
            }else{ 
                if(next % (increment*10) == 0) {
                    ranges.push(next);
                    increment = higher ? increment*10 : increment/10;
                }
            }

            if(!higher && increment < 10) {
                break;
            }
        }

        ranges.push(to + 1);
        var regex = '/^(?:';

        for(var i = 0; i < ranges.length - 1; i++) {
            var str_from = ranges[i];
            str_from = str_from.toString();
            var str_to = ranges[i + 1] - 1;
            str_to = str_to.toString();
            for(var j = 0; j < str_from.length; j++) {
                if(str_from[j] == str_to[j]) {
                    regex += str_from[j];
                }
                else {
                    regex += "[" + str_from[j] + "-" + str_to[j] + "]";
                }
            }
            regex += "|";
        }

        return regex.substr(0, regex.length - 1 ) + ')$/';
    }