I'd like to perform an action (while I'm presenting a Google Slides App) each time I progress from one slide to another. Is there such a trigger? If there isn't how could I implement that?
Looking at the progress example (https://github.com/googlesamples/apps-script/blob/master/slides/progress/progress.gs) that's just generates the progress bar into each slide during installation.
No, there isn't. Unfortunately Google Apps Script hasn't a built-in feature to implement custom-triggers.
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