How do I get the value of checkboxes of custom columns

I made a table and added an extra column, a checkbox. I don't know how to find out if that checkbox is checked or not {{}} does not have the extra column in it.

Hi Noz!

Custom columns are essentially "frontend" so they're not accessible in or table1.selectedRow.

If a custom column is edited (ie a checkbox is checked), then the values will show up in table1.recordUpdates! The first checkbox checked (which may not necessarily be the first row) will be accessible like {{table1.recordUpdates[0]['Custom Column 1']}}.
Would that work for you?