How to use loop through with js?

[Timo Mikkolainen]

I'm trying to make a simple-ish script that adds an edge loop to the
selected object.
The only part missing is the edge 'ring' selection, i.e.
<ctrl>+<shift>+loop tool. I'm having a hard time finding any
references to this in the js files. Apparently it should be in
sdsplus, but things there look mighty empty.