[whichdan]

Tiny suggestion - instead of

  .map(g => { return { key: g.key, rows: g.rows.map(r => r[1]) }})

you can write

  .map(g => ({ key: g.key, rows: g.rows.map(r => r[1]) }))

[rcarr]

You could also destructure g to end up with:

.map(({ key, rows }) => ({ key, rows: rows.map(r => r[1]) }))

[nivertech]

also:

  .map(({ key, rows }) => ({ key, rows: rows.map(([page, link]) => link) }))

and

  .groupBy(p => p[0])

to

  .groupBy(([link, file]) => link)