unordered-set/index.js

A couple of functions that make it easy to maintain an unordered set as an array in an efficient way

exports.add = add
exports.has = has
exports.remove = remove
exports.swap = swap

function add (list, item) {
  if (has(list, item)) return item
  item._index = list.length
  list.push(item)
  return item
}

function has (list, item) {
  return item._index < list.length && list[item._index] === item
}

function remove (list, item) {
  if (!has(list, item)) return null

  var last = list.pop()
  if (last !== item) {
    list[item._index] = last
    last._index = item._index
  }

  return item
}

function swap (list, a, b) {
  if (!has(list, a) || !has(list, b)) return
  var tmp = a._index
  a._index = b._index
  list[a._index] = a
  b._index = tmp
  list[b._index] = b
}