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When the Upload is in its asynchronous mode, the association between the files and the context they originate from is normally lost.

For example, in an application, the save handler has to associate the uploaded files with a specific message. The message and the file might be processed on different servers in a load-balancing or cloud-computing scenario.

The described approaches for sending and receiving metadata are also applicable to the remove handler.

Sending Metadata

To send metadata over to the save handler:

  1. Add an input field for the file description whose value will be sent to the save handler.

    <input type="text" id="fileDescription" />
  2. Declare a handler for the upload event and attach a data object to the passed event.

    function onUpload(e) { = {
            fileDescription: $("#fileDescription").val()
  3. Attach the upload event handler.

        async: {
            saveUrl: "saveHandler.php",
            removeUrl: "removeHandler.php"
        upload: onUpload
  4. Process the file and the associated description. The description and any other fields of the object will be serialized in the POST request. For more information on how to read posted form fields, refer to the documentation of your server-side platform.

Receiving Metadata

The save handler can sometimes produce a result that needs to be routed back to the page. The Upload requires a response in a JSON format with a Content-Type set to "text/plain". Responses that are not empty and in a format other than JSON will be treated as a server error.

To receive metadata from the save handler:

  1. Build the response.

        header('Content-Type: text/plain;');
        $data = array('foo' => 'bar', 'status' => 'ok');
        echo json_encode($data);
  2. Declare a handler for the success event and process the response.

    function onSuccess(e) {
        alert("Status: " + e.response.status);
  3. Attach the event handler.

        async: {
            saveUrl: "saveHandler.php",
            removeUrl: "removeHandler.php"
        success: onSuccess

See Also

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