Question

For some reason ajax is not sending data.

On the PHP I have this code:

if (isset($_POST['submit'])) { 
    echo "submit";
} else {
    echo "not submit";
}

And I get not submit.
This is JS code:

$(function () {
    $('#submit').click(function () {
        var length = $('#number').val();
        var small = $('#small').val();
        var big = $('#big').val();
        var number = $('#numero').val();
        var special = $('#special').val();
        var submit = 'submit';
        var url = 'public/php/codegenerator.php';
        var data = "length=" + length + "&small=" + small + "&big=" + big +
                   "&number=" + number + "&special=" + special + "&submit=" + submit;

        $.ajax({
            type: "POST",
            url: url,
            data: data,
            success: function () {
                $('#code').load(url, function () {
                    $(this).fadeIn(1000)
                });
            }
        });
        return false;
    });
});

Answer 1

You can try this approach

$(function(){
    $('#submit').click(function(){
        //YOUR CODE

       var param = {
            length:length,
            small:small,
            big:big,
            number:number,
            special:special,
            submit:submit
        }

         $.ajax({
            type: "POST",
            url: url,
            data: param,   

            //EDITED LINE     
            success: function (data) {
                $('#code').hide().html(data).fadeIn(1000);
            }               
        });       
        return false;
    });               
});

// REVISED ANSWER

// IN YOUR PHP FILE

if (isset ($_POST['submit'])) { 
    echo json_encode(array('result'=>"submit"));
}
else {
    echo json_encode(array('result'=>"not submit"));
}

//IN YOUR JQUERY CODE

$.ajax({
    type: "post",
    url: url,
    data: param, 
    dataType:'json';  

    //EDITED LINE     
    success: function (data) {
        // alert(data.result);
        $('#code').hide().html(data.result).fadeIn(1000);
    }               
});