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Obsolescence of links for participants

Dear Jatos,

First of all, thank you for offering such an amazing tool as JATOS, plus the free server... dreams come true.

I have a question about the durability of links we send to participants. It happened a few times that the links I sent would be deprecated with the message "the study can only be done once" or stuck at the "loading" screen (I used lab.js for building the study).

So since the study is a questionnaire that is a bit longer than 40 minutes, I'm concerned that it could be an issue for the data collection... How can I ensure that each participant get a valid link ?

Thank you for your help.

Best wishes,



  • Hi Victor,

    Happy to hear you're finding JATOS useful!

    Links don't expire over time. As long as a participant clicks on the link once and doesn't reload, it will always work.

    Personal-single or General-single links can be used only once, which is the error message you're seeing. If you want to have no restrictions on the number of times the same participant uses a link, you could use a General-multiple link. (I know, the naming is not great).

    Hope this helps


  • Thank you for your answer Elisa. Now I have a second Issue, the experiment won't open and there is only a screen with the message "loading experiment" (lab.js) on it... I'mm quite confused at this point

  • Without more information, it's hard to know what the problem is.

    If you open the Developer tools in the browser, do you see any error messages in the console? What did you change that made it not work anymore? Does it work with some worker types and not others?


  • Yes of course.

    So here is the screen i get.

    And the errors that occured :

    it's a 404 error code."Failed to load ressources"

    Thank you for your help

  • Looks like your study misses some files (the red error messages in your screenshot). The yellow warnings you can ignore. Can you imagine why there are some files missing or can't be loaded? Maybe you use wrong paths?

    Buy Me A Coffee

  • edited July 2020

    Dear kri, thank you for your answer

    I actually don't have any file attached to my study... The only thing that could interfere here is the fact that the study was built on lab.js. But it actually used to work. It doesn't anymore and I really don't know why.

    Now i have a 403 error...

  • Hi Victor,

    It's hard to help without more details. So here come a few questions:

    -What changed between the time it worked and when it stopped working?

    -Why changed between the 404 and 403 errors?

    -What happens if you re-export the study from lab.js? Will that work then?


  • I'm sorry for not being really efficient in my questions ... I'll do better :)

    -What changed between the time it worked and when it stopped working?

    Literally nothing. Time passed. Then I tried to re-export/upload the study from lab.js a few times, with no success ...

    -Why changed between the 404 and 403 errors?

    Good question... I didn't change the experiment between yesterday and today...

    -What happens if you re-export the study from lab.js? Will that work then?

    I did the export one more time here and nothing changed, i still have the same error.

    The only thing is that when I import the study on Jatos, I get that message, suggesting that I have a directory for another study on the server, even though i deleted all before... I have this message every time.

    Thank you for your help

  • I just wonder: Who gave your study's assets folder the name 'study', lab.js or yourself? It's not wrong, it's just a very generic folder name and it's likely that it will collide with some different study on your server that has the same asset folder name.

    And this weird study asset folder naming confusion could also explain the problem you are experiencing with some files not being able to load. JATOS can deal with same assets folder. Like in the message you posted: JATOS can rename them. But this can lead to your study not being loaded properly because your lab.js study looks into the wrong folder.

    I'd strongly suggest to give your study a more unique name: something like study-to-test-the-foo-effect.

    Buy Me A Coffee

  • Just like you said kri, the name comes from the lab.js export. I tried to rename the folder from that export (that I have to unzip/rezip). But then the Jatos server doesn't recognize it anymore... Puzzling.

    The name of that folder is not editable in the lab.js interface.

    Thank you for your help... I hope I'll be able to do it after all

  • Dear Kri and Elisa,

    I finally found the way to change the name of the study on the Lab.js builder. So here we have it !

    Thank you very much for your help !


  • Always happy to help!

    Buy Me A Coffee

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