Custom sampling: how to sample one stimulus of a pair(from a set of pairs)?

[Alinaedr]

Hello,

I've been trying to figure out how to write a sampling function for my experiment, but haven't found a clean way to do it so far. My code looks like this:

var trial1 = {
        type: jsPsychHtmlSliderResponse,
        timeline: [
            {stimulus: jsPsych.timelineVariable('stimulus')}
        ],
        timeline_variables: [
                {stimulus: 'some stimulus A',
                 context: '1'},
                {stimulus: 'some stimulus B',
                 context: '2'}
            ],
            sample: {
                type: 'without-replacement',
                size: 1
            },
        require_movement: true,
        labels: ['0% chance', '50% chance', '100% chance'],
        data: {
            name: jsPsych.timelineVariable('name'),
            context: jsPsych.timelineVariable('context')
        }
    }
    timeline.push(trial1)

    var trial2 = {
        type: jsPsychHtmlSliderResponse,
        timeline: [
            {stimulus: jsPsych.timelineVariable('stimulus')}
        ],
        timeline_variables: [
                {stimulus: 'some stimulus C',
                 context: '1'},
                {stimulus: 'some stimulus D',
                 context: '2'}
            ],
            sample: {
                type: 'without-replacement',
                size: 1
            },
        require_movement: true,
        labels: ['0% chance', '50% chance', '100% chance'],
        data: {
            name: jsPsych.timelineVariable('name'),
            context: jsPsych.timelineVariable('context')
        }
    }
    timeline.push(trial2)

And there are 40 trials of this same type. As you can see, every trial samples one out of two available timeline variables (two stimuli in the pair), because I need only one of each pair to be sampled (only one of two contexts for each pair should appear). Is there a function I could write to make this process more automatic (rather than copying and pasting all the trial information for each pair)?

Any help would be greatly appreciated!