core.wait() is a PsychoPy function that doesn’t exist in PsychoJS. Having said that, core.wait() should never be used in a Builder experiment, only in Python scripts that are crafted by hand. Builder scripts are structured around a drawing and event loop that assumes that any code that runs can be completed within one screen refresh (typically at 60 Hz this is 16.666 ms), because Builder is actively drawing to the screen on every refresh, checking for responses and so on, even if stimuli don’t appear to be changing. core.wait() breaks this active drawing cycle and can completely muck up Builder’s internal timing. You should restructure your experiment to avoid core.wait(). The translation to PsychoJS should then hopefully be straightforward.