Slider not updating visualization

Hey @Bryan, thank you for your response! I don’t understand how to change the source.data if all that is being passed are parameters to the callback function. After looking at the documentation that you kindly linked, the example titled “CustomJS for Model Property Events” appears to have similar JS code to my example. The code is also creating local variables x and y, with an added for loop.

How do we reassign source.data in the call back function?