Automatically get values of all element inside a div with jQuery

Try something like that:

function getAllValues() {
  var allVal = '';
  $("#mainDiv > input").each(function() {
    allVal += '&' + $(this).attr('name') + '=' + $(this).val();
  });
  alert(allVal);
}

To achieve this you can select all the form fields and use map() to create an array from their values, which can be retrieved based on their type. Try this:

function getAllValues() {
    var inputValues = $('#mainDiv :input').map(function() {
        var type = $(this).prop("type");

        // checked radios/checkboxes
        if ((type == "checkbox" || type == "radio") && this.checked) { 
           return $(this).val();
        }
        // all other fields, except buttons
        else if (type != "button" && type != "submit") {
            return $(this).val();
        }
    })
    return inputValues.join(',');
}

The if statement could be joined together here, but I left them separate for clarity.