function changeUrl(base, find, value) {

    var offset = base.indexOf(find);

    var index;

    var rr = '';

    if(offset < 0){

        if(base.indexOf('?') < 0) {

            base += '?';

        }else{

            base += '&';

        }

        base += find + '=' + value;

    }else{

        left = base.substr(0, offset);

        right = base.substr(offset);

        index = right.indexOf('&');

        if(index >= 0){

            rr = right.substr(index);

        }

        base = left + find + "=" + value + rr;

    }

    return base;

}

console.log(changeUrl('http://www.car.dev/?per_page=2&ano=3&dis=1', 'ano', 4));