function trim() {

    var start, end;

    start = 0;

    end = this.length - 1;

    while(start <= end && this.charAt(start) == " " ) {

        start ++;

    }

    while(start <= end && this.charAt(end) == " " ) {

        end --;

    }

    return this.substring(start, end+1);

}

function reverse() {

    var str = "";

    var end = this.length - 1;

    for(;end >= 0; end --) {

        str = str + this.charAt(end);

    }

    return str;

}

String.prototype.trim = trim;

String.prototype.reverse = reverse;