Unknown javascript error

URL of experiment:

Description of the problem:
when trying the study online I always get the same error : unknown java error. I’m searching to fix this since many many hours and read on internet. I see that a lot of people encounter this problem but without response to fix it. I always have the same issue. first time it was probably due to rating scale. so I switch on “slider”. that runs fine on the standalone psychopy but clearly not online. I had a look on online study. it seems that a file beginning by “Dzialajace…” is missing in my files. I don’t find how to create it…
could you help me?


I see “dialog” in your error stacktrace. Perhaps there is an issue with the experiment info? (that’s the dialog box shown at the start of the experiment)

thanks Thomas, but I don’t see what the problem is. here is the screen captures about experiment setting. the only uncertainty I have is about the data part but it seems that this is automatically completed and very difficult to understand the rules about that. I join the four screenshot concerning the setting as stereo is not usefull in this experience…
thanks for your help. i really appreciate as it helps me to be more efficient under psychopy instead of eprime :slight_smile:

I spot nothing suspicious in your screenshots. Could you share the experiment with me so I can take a look? My gitlab username is tpronk. Here are some instructions on how to give me access: Unable to download resource

Hi Thomas
You are now maintainer of this experiment. thanks for your help.

Hi Carole,

I took a look and something is going wrong with slider2, but I’m not sure what the problem is. I asked for some help of my team; update soon!

Best, Thomas

Hello Thomas,@thomas_pronk , do you have some news about this problem from your teams? thanks

Hi @carole, sorry for the delay. I asked again

Hello thomas, I add you to the same project but called test1. this is exactly the same but uploaded through a PC! I don’t know why, but the experiment run correctly. I try to figure out why because it s problematic to have some issues with mac and not with a PC. Could you have a look? maybe you will find more quickly than me what s going on :slight_smile:

Sorry; I didn’t really get what the problem was in the first place, so it would be hard for me to find out what solved it :). Still, nice that it works again! Got a hunch: maybe you exported for the most recent version of PsychoPy?

Hello @carole,

I tried to have a look at your experiment yesterday but it appears that you deleted it.
Did you manage to solve the issue? I would be happy to have a look.
Best wishes,


Hello Alain
no, there is 3 experiments. one called “experiment 1”.this one doesn’t function at all (unknown error). there is a second one called “test1” and a third one called “test2”. these two last function perfectly when launch with a PC but not on a macbook. the first doesn’t work with both system. So, I guess there is a compatibility problem under mac when creating the experiment (there is a file missing in the folder: index.html). when I have push test 1 and test2 on pavlovia, all run correctly. I add your id on both studies so you could have a look…I would be very interested if someone using a mac succeed to launch test1 or test2 because I fear that mac user couldn’t participate to this study…best regards

Hello @carole,

I believe I have sorted the experiment1 issue. It had to do with your using slider labels which were numbers instead of text. I have just modified the PsychoJS library such that numerical labels are automatically converted to text, and your experiment is now working.
I am not sure about the issue with running test1 and test2 on macs. I would encourage you to post another message on the forum with that specific issue. I am sure someone will be able to assist you.
Best wishes,


can you also help me Thomas?

Hello Alain,
unfortunately, I can’t run the experiment 1 (with my mac). I will try with my PC this evening (I will edit my post in accordance). for numerical labels, what do you suggest with using slider in psychopy builder? I have some difficulties to figure out how to obtain number on each slider tick, without entering numbers in the label box of the slider properties.thanks :slight_smile: