Stuck on INITIALISING THE EXPERIMENT. "Favicon" error in Java console

URL of experiment:

Description of the problem:
I have been trying to run an online experiment (generate with the Psychopy Builder, latest version) in Pavlovia, but it gets stuck at the initialisation page. The experiment is essentially identical to another one, which still works fine in Pavlovia. The only difference is that, in the current one, I use videos instead of images.

There are a few code components, but I also added a “code_JS” component in my first routine, as described here.

The error reported in my bowser console is the following:

[Exception… “Favicon at “” failed to load: Not Found.” nsresult: “0x80004005 (NS_ERROR_FAILURE)” location: “JS frame :: resource:///modules/FaviconLoader.jsm :: onStopRequest :: line 241” data: no]

Many thanks in advance,


I found the problem. I had a text component with no text in it, which somehow generated a comma (,) in the .js file, which Pavlovia didn’t like apparently.

Hi There,

When I click the link to your experiment it manages to initialize ok but I do get the error * ReferenceError: randint is not defined

Did you manage to resolve your original issue?

Hi Becca,

thanks for your reply.

Yes, I resolved the original issue, but not this new one about “randint”, which I’ve actually defined in my code_js component, at the beginning of the experiment. Not sure why it doesn’t like it.



Please could you show your randint definition code?


randint = function(min, maxplusone) {
  return Math.floor(Math.random() * (maxplusone - min) ) + min;

Thanks. I’ve just had a look at your JS code and it doesn’t appear.

However, having downloaded your .psyexp file my conclusion is that the code_JS code has to go in Begin Experiment and not Before Experiment.

Before Experiment is a new tab which didn’t exist when I first started working on my crib sheet.

Hello there, thanks for your reply.

I’ve just moved everything to Begin Experiment, but, weirdly enough, it now gets stuck at the “initialising the experiment” page.

Identifier ‘abs’ has already been declared

You should remove definitions of abs, sin, cos, PI: pi, sqrt from code_JS

Yes, you’re right, thanks a lot.

The experiment now starts fine, but then it produces an unknown error message when it should display the videos.

Anyway, I’ll have a go at it. Many thanks again.

I think that’s because you’re using .mov video format. Try H.264 encoded MP4 files with AAC audio encoding.

Ok, thanks.

I had originally generated the videos with the coder as MP4 files, H.264, although, as I couldn’t find an obvious way to change the resolution from 2800x1880 to a lower resolution with the coder (in order to be displayed at the right speed with the Builder), I used Quicktime to change the resolution, but I could only save the files as .mov.

Do you know how to change the resolution with the coder when you’re generating a video?