Monday, April 9, 2012: Fluid (Mac): Fix Back Button Breaking the JavaScript API

While I was making dtinthstagram, I thought that it would be a good idea to make it work in Fluid, as well as a support for dock badges.

So I implemented it in a straightforward way. Then I found that going to other page and back to the old page breaks the Fluid JavaScript API.

When navigating to another page, the API gets destroyed. When the user return back to the old page, calls to the API generates an error:

ReferenceError: Trying to access object from destroyed plug-in.

I contacted the developer of Fluid, but for now, I came up with a workaround that works pretty well.

I fixed the problem by checking, if invoking the Fluid API generates an error, then create a hidden iframe (which Fluid will initialize another JavaScript API instance inside it), and then use the API of the iframe instead.

The code goes like this (comments added):

// holds the reference to the window
// that holds the Fluid JavaScript API.
var fluidHoster = window;

// the iframe instance, if any.
var fluidIframe = null;

// the text queued to show on the dock badge.
var fluidQueuedText = null;

function setDockBadge(text) {
    if ('fluid' in window) {
        try {
            if (fluidHoster == null) {
                // the iframe did not finish loading, queue the text
                fluidQueuedText = text;
            } else {
                // try calling the API
                fluidHoster.fluid.dockBadge = text;
        } catch (e) {

            // in case of error, queue the text,
            fluidHoster = null;
            fluidQueuedText = text;

            // trash the old iframe,
            if (fluidIframe != null && fluidIframe.parentNode) {

            // create a new iframe,
            var iframe = fluidIframe = document.createElement('iframe');

            // make it display the queued text on the dock
            // when the API is ready
            iframe.onload = function() {
                fluidHoster = iframe.contentWindow;
                fluidHoster.fluid.dockBadge = fluidQueuedText;

            // add to document.body
            iframe.src = 'about:blank';
   = 'none';