Form values are not found from form in jQuery?

I have made my own jQuery plugin, but it has problem that values I set in form are not found in form when I try to generate query string from form. Test it here http://jsfiddle.net/z3Yff/3/.

(function($) {

    $.fn.ajaxSubmit = function( options ) {
        // Plugin settings
        var settings = {
            beforeFunction : function() {},
            afterFunction : function() {}
        };

        // Override options
        if ( options ) { 
            $.extend( settings, options );
        }

        // Set variables
        var self = this;

        // Check that form value is set
        var checkValue = function(value) {
            if(value != undefined && value != null)
            {
                return true;
            }
            return false;
        };

        // Catch submitting input/button
        var submitInputName;        
        $("button, input[type=submit]", this).live("click", function() {
            submitInputName = $(this).attr("name");
        });

        // Submit form
        var submitForm = function(form) {        
            var method = form.attr("method");
            if(!checkValue(method) || method.length == 0) method = "post";
            var action = form.attr("action");
            var query = "";
            var i = 0;
            $("input, button, textarea", $(this)).each(function(index) {
                var name = $(this).attr("name");
                var value = $(this).attr("value");
                var type = $(this).attr("type");
                if(checkValue(value) && checkValue(name))
                {
                    if(i > 0)
             开发者_如何学编程       {
                        query = query + "&";
                    }
                    query = query + name + "=" + value;
                    i++;
                }
            });
            alert(query); // This is empty String, but it should contain values I enterd to form
            return $.ajax({
                type: method,
                cache: false,
                url: action,
                data: query,
                async: false
            }).responseText;
        };

        // Add ajax submit catching
        this.submit(function() {
            options.beforeFunction();
            submitForm($(this));
            options.afterFunction();
            return false;
        });
    };

})(jQuery);

Your immediate problem is in your checkValue function. This conditional will always be false:

if(value != undefined && value != null && name != undefined && name != null)

because you're not passing name into the function; the above is logically equivalent to this:

var name;
if(value != undefined && value != null && name != undefined && name != null)

Just as a style note, you could write it as:

function checkValue(value) {
    return typeof value != 'undefined' && value != null;
}

There is no special undefined value or keyword in JavaScript. When you say x != undefined you're actually implicitly creating a variable called undefined that is not initialized, hence the typeof value != 'undefined' instead of your value != undefined.

There are other problems. For one, you're skipping over <select> elements. For another, you're not checking the type of <input> elements so you'll include the values of checkboxes and radio buttons that are in the form but not selected.

Furthermore, you're using the wrong thing in your .each, you want $(form) rather than $(this) so this:

$("input, button, textarea", $(this)).each(function(index) {

should be this:

$("input, button, textarea", $(form)).each(function(index) {

I didn't fix the <select>, radio button, or checkbox issues but this version is at least producing a query string: http://jsfiddle.net/ambiguous/8QYWH/