Preload fails for path specified in call function

[GAldegheri]

Hi, in my experiment I'm trying to preload an image which is set from a call function.
This fails, giving me "Error loading file".
It seems however that the image path is visible from the preloading node, i.e. if I use a on_start function to print it, it's printed correctly.
But it cannot load it for some reason.
Here is a minimal code example that reproduces this issue:

  var stimulus = '';

  var setstimulus = {
    type: 'call-function',
    func: function(){stimulus = 'image.png';}
  };

  var preload_trial = {
    type: 'preload',
    images: [stimulus],
    show_progress_bar: false,
    show_detailed_errors: true,
    on_start: function(){console.log(stimulus);}
  };

  jsPsych.init({
      timeline: [setstimulus, preload_trial]
  });

Is this issue known with call functions?

[jodeleeuw]

Hi @GAldegheri

At the time that preload_trial is declared stimulus is still ''. The call-function trial doesn't run until after the experiment is initialized, at which point the value of stimulus is updated.

To use that updated value for preload_trial, you need to use dynamic parameters.

[GAldegheri]

Thanks for your reply, it works!