timeline variables with nested objects

[CrumpLab]

I've been trying to use timeline variables that contain nested objects. For example, I modified this from the example documentation on timeline variables. Here, I would be attempting to populate the stimulus say with the info contained in the props.type part of the timeline array.

But, this doesn't seem to work. I'm probably missing something like a syntax issue here. Is there a workaround?

var face_name_procedure = {
    timeline: [
        {
            type: 'html-keyboard-response',
            stimulus: jsPsych.timelineVariable('props.type'),
            choices: jsPsych.NO_KEYS,
            trial_duration: 2500
        }
    ],
    timeline_variables: [
        { face: 'person-1.jpg' , props: {type: 'A', condition: 'A'}},
        { face: 'person-2.jpg' , props: {type: 'B', condition: 'A'}},
        { face: 'person-3.jpg' , props: {type: 'C', condition: 'B'}},
        { face: 'person-4.jpg' , props: {type: 'D', condition: 'B'}}
    ]
}

[jodeleeuw]

The string that is passed to jsPsych.timelineVariable() is used to match keys in the object. props is a valid key, but props.type is not since you would need to extract the props object and get its type key.

You can workaround by customizing how you invoke the timelineVariable function:

{
  stimulus: function() { 
    var props = jsPsych.timelineVariable('props', true); // true argument means evaluate immediately
    return props.type;
  }
}

[CrumpLab]

Woohoo!! Thanks for the quick reply, my lack of js basics was driving me nuts.