FileUploader.js

dojo.require("dijit._Widget");

dojo.declare("FileUploader", dijit._Widget, {

    ID_KEY         : 'APC_UPLOAD_PROGRESS',
    statusUrl      : 'status.php',
    pollDelay      : 500,  // in milliseconds

    form           : null, // HTML form element
    status         : null, // element where the upload status is displayed
    statusTemplate : null, // Prototype Template object
    idElement      : null, // element that holds the APC upload ID
    iframe         : null, // iframe we create that form will submit to

    constructor : function(form, status)
    {
        // initialize the form and observe the submit element
        this.form = dojo.byId(form);
        this.connect(this.form, "onsubmit", "_onFormSubmit");

        // create a hidden iframe
        this.iframe = dojo.create('iframe', { name : '_upload_frame', style: { display: 'none' } });

        // make the form submit to the hidden iframe
        this.form.appendChild(this.iframe);
        this.form.target = this.iframe.name;

        // initialize the APC ID element so we can write a value to it later
        this.idElement = this.form[this.ID_KEY];

        // initialize the status container
        this.status = dojo.byId(status);

        // clear the status template
        this._updateStatus();
    },

    generateId : function()
    {
        var now = new Date();
        return now.getTime();
    },

    _onFormSubmit : function(e)
    {
        var id = this.generateId();

        this.idElement.value = id;
        this._monitorUpload(id);
    },

    _monitorUpload : function(id)
    {
        dojo.xhrPost({ url: this.statusUrl,
                       content: { id: id },
                       load: dojo.hitch(this, "_onMonitorSuccess"),
                       handleAs: "json"
                     });
    }, 

    _onMonitorSuccess : function(resp)
    {
        var json = resp;

        dojo.style(this.status, "display", "block");
        
        var theHtml = ...; // build your status html from the JSON
        this._updateStatus(theHtml);

        if (!json.finished) {
            window.setTimeout(dojo.hitch(this, "_monitorUpload"), this.pollDelay);
        }
    },

    _updateStatus: function(theHtml)
    {
      this.status.innerHTML = theHtml;
    }
});