SOURCE

var intersection = function (nums) {
  const map = {}
  const l = nums.length
  nums.forEach(item => {
    item.forEach(c => {
      if (!map[c]) {
        map[c] = 1
      } else {
        map[c]++
      }
    })
  })
  return Object.entries(map).filter(item => item[1] === l).map(item => item[0]).sort((a, b) => a - b)
};
console.log(intersection([[3,1,2,4,5],[1,2,3,4],[3,4,5,6]]))