[SuperZen]

let arrs = [[1, , 3, 4, 5,], [, 2, 3, 4, 5, 234,], [, , ,]];
console.log(
  arrs.reduce((acc, cur) => {
    let items = cur.filter(item => item !== null)
    items.length && acc.push(items)
    return acc
  }, [])
)