I can find a div that has an attribute like so:
$(\'.funding-plan-container[data-timestamp]\')
But if I try to find a div that does not hav
Use the :not() selector.
$('.funding-plan-container:not([data-timestamp])')
This, by the way, is a valid Selectors API selector, so it isn't specific to jQuery. It'll work with querySelectorAll() and in your CSS (given browser support).
querySelectorAll()