The idea is:
Currently you can’t seem to drag inputs from a previous node (that are displayed in the left panel when editing a node) to a place in the code of a function node.
EDIT: for those stumbling on this post, assuming it hasn’t been implemented yet: you can switch the left panel to ‘json’ and then select the line you want. Click the clipboard icon, that way you can copy paste it into your code
I think it would be beneficial to add this because:
It seems quicker to be able to drag input than to type it.