Dynamically load image with different GET parameters

Question

I'm trying to load an image (created with PHP) with jQuery and passing a few variables with it (for example: picture.php?user=1&type=2&color=64). That's the easy part.

The hard part is that I've a dropdown which enables me to select background (the type parameter) and I'll have an input for example to select a color.

Here're the problems I'm facing:

1. If a dropdown/input hasn't been touched, I want to leave it out of the URL.
2. If a dropdown/input has been touched, I want to include it in the url. (This won't work by just adding a variable "&type=2" to the pre-existing string as if I touch the dropdown/input several times they'll stack (&type=2&type=2&type=3)).
3. When adding a variable ("&type=2" - see the code below) to the pre-existing URL, the &-sign disappears (it becomes like this: "signature.php?user=1type=2").

Here's the code for the jQuery:

<script>
    var url = "signatureload.php?user=<?php echo $_SESSION['sess_id']; ?>";

    $(document).ready(function() {
        window.setTimeout(LoadSignature, 1500);
    });

    $("#signature_type").change(function() {
        url += "&type="+$(this).val();

        LoadSignature();
    });

    function LoadSignature()
    {
        $("#loadingsignature").css("display", "block");
        $('#loadsignature').delay(4750).load(url, function() {
            $("#loadingsignature").css("display", "none");
        });
    }
</script>

Here's the code where I load the image:

<div id="loadsignature">
    <div id="loadingsignature" style="display: block;"><img src="img/loading-black.gif" alt="Loading.."></div>
</div>

I don't know how more further I could explain my problem. If you have any doubts or need more code, please let me know.

Thank you for your help!

EDIT:

Here's the current code:

<script>
    var url = "signatureload.php?user=<?php echo $_SESSION['sess_id']; ?>";

    $(document).ready(function() {

        window.setTimeout(LoadSignature, 1500);

    });

    $("#signature_type").change(function() {
        url = updateQueryStringParameter(url, 'type', $(this).val());

        LoadSignature();
    });

    function LoadSignature()
    {
        $("#loadingsignature").css("display", "block");
        $('#loadsignature').delay(4750).load(url, function() {
            $("#loadingsignature").css("display", "none");
        });
    }

    function updateQueryStringParameter(uri, key, value)
    {
        var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i"),
        separator = uri.indexOf('?') !== -1 ? "&" : "?",
        returnUri = '';

        if (uri.match(re))
        {
            returnUri = uri.replace(re, '$1' + key + "=" + value + '$2');
        }
        else
        {
            returnUri = uri + separator + key + "=" + value;
        }

        return returnUri;
    }
</script>

EDIT2:

Here's the code for signatureload.php

<?php
    $url = "signature.php?";

    $count = 0;
    foreach($_GET as $key => $value)
    {
        if($count > 0) $url .= "&";
        $url .= "{$key}={$value}";
    }

    echo "<img src='{$url}'></img>";
?>

Answer 1

If I understood your question correctly, it comes down to finding a proper way of modifying GET parameters of the current URI using JavaScript/jQuery, right? As all the problems you point out come from changing the type parameter's value.

This is not trivial as it may seem though, there are even JavaScript plugins for this job. You could use a function like this and in your signature_type change event listener,

function updateQueryStringParameter(uri, key, value) {
    var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i"),
        separator = uri.indexOf('?') !== -1 ? "&" : "?",
        returnUri = '';

    if (uri.match(re)) {
        returnUri = uri.replace(re, '$1' + key + "=" + value + '$2');
    } else {
        returnUri = uri + separator + key + "=" + value;
    }

    return returnUri;
}

$('#signature_type').change(function () {

    // Update the type param using said function
    url = updateQueryStringParameter(url, 'type', $(this).val());

    LoadSignature();
});