Experiment sometimes not sending data

[Julie Gerard]

Hello,

I've run 2 iterations of an experiment on Prolific, and the first one sent the data to my server for 80% of the participants, while the second one sent the data for just 40% of the participants. For the participants where the data did send, I have all of their data for all of the trials; it's the ones that didn't send any data that I can't figure out - there is no data file at all for these participants.

There is no javascript error when the 'submit' button is clicked, althought I do sometimes get the error when I start the experiment "The AudioContext was not allowed to start. It must be resumed (or created) after a user gesture on the page." I didn't think this should be an issue, though, since there is not audio input from the participant in the experiment.

All of the participants must have clicked 'submit', since this was the only way to return to Prolific via the url with the completion code.

Could this be a browser issue?

Here is my code for sending the data to the server, and the jspsych.init portion:

function saveData(name, data){

  var xhr = new XMLHttpRequest();

  xhr.open('POST', 'write_data.php'); // 'write_data.php' is the path to the php file described above.

  xhr.setRequestHeader('Content-Type', 'application/json');

  xhr.send(JSON.stringify({filename: name, filedata: data}));

  window.location = "this was the Prolific URL with the completion code";

}

timeline.push(instructions,pro_id,procedure,final)

                var timestamp = Date.now();

jsPsych.init({

timeline: timeline,

on_finish: function(){ saveData(timestamp, jsPsych.data.get().csv()); }

})

[Mara Haslam]

Julie,

This is a wild guess, but are your participants all using the php file at the same time?  If so, it might be busy processing one person's data so that another person's data doesn't get saved.

I had an error like this in my experiments and I solved it with a web worker.

Mara

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[Josh de Leeuw]

I think this is because some participants are being redirected to prolific before the XMLHttpRequest is sent. XMLHttpRequests are asynchronous, so the window.location part of the code may execute before the request makes it to the server. 

You could put the 

window.location = "this was the Prolific URL with the completion code"; 

part of the code inside the onload callback:

xhr.onload = function() {

 window.location = "this was the Prolific URL with the completion code"; 

}

To view this discussion on the web visit https://groups.google.com/d/msgid/jspsych/CAAdNNLE1WtQzoHrguLDRSQ_cq5%3Dw2Km1jLinQQMmWVEtv2d6Cw%40mail.gmail.com.

[Julie Gerard]

Thank you!

Yes, putting the window.location call inside the onload callback fixed the issue, 100% of data sent now.

[philip....@york.ac.uk]

A bit of a dull question but in my data saving function copied from jspsych

function saveData() { 

  var xhr = new XMLHttpRequest(); 

   xhr.open('POST', 'write_data.php'); // change 'write_data.php' to point to php script. 

  xhr.setRequestHeader('Content-Type', 'application/json'); 

  xhr.onload = function() { if(xhr.status == 200){ var response = JSON.parse(xhr.responseText); console.log(response.success); } }; xhr.send(jsPsych.data.get().json()); }

The onload call comes before the send call so how does it know to redirect the user only once the send has completed.

Thanks in anticipation,

Philip.

[Josh de Leeuw]

Hi Philip,

The xhr.onload = function() { ... } line sets up an event handler. This is just establishing what the XMLHttpRequest should do when it loads. The send() begins the execution process, which will eventually trigger the load event.

Cheers,

Josh

To view this discussion on the web visit https://groups.google.com/d/msgid/jspsych/e0b53e29-97bc-4362-befd-cf423e28df58n%40googlegroups.com.

[philip....@york.ac.uk]

Thanks Josh I am new to callbacks and struggling a bit.

Best regards,

Philip.