import { foldclosed } from "https://deno.land/x/denops_std@v6.4.0/function/mod.ts";
The result is a Number. If the line {lnum} is in a closed
fold, the result is the number of the first line in that fold.
If the line {lnum} is not in a closed fold, -1 is returned.
{lnum} is used like with getline(). Thus "." is the current
line, "'m" mark m, etc.
Can also be used as a method:
GetLnum()->foldclosed()
Parameters
denops: Denops