Question

How do you find if the response contains the element form

    $.ajax({
        url     : $(this).attr('action'),
        type    : 'POST',
        success : function(response){
            if($(response).find('form').length)
            {
                alert("hii");
            }
        }
    });

Form could be the topmost element of the response or somewhere in middle

Answer 1

$.ajax({
        url     : $(this).attr('action'),
        type    : 'POST',
        dataType: 'html', // you should set it 
                          //  if you response send html only
        success : function(response){
            if($(response).filter('form').length)
            {
                alert("hii");
            }
        }
    });

According to update:

        ....
        dataType: 'html',
        success : function(response){
            var container = $('<div/>').append(response);
            if($(container).find('form').length)
            {
                alert("hii");
            }
        }