Flux pattern: How to update an item in an Array in an immutable way

update.js

function update (state, data) {
  var active = state.active.concat()
  var i = 0
  var l = active.length
  var item
  for (i; i<l; i++) {
    item = active[i]
    if (item.id === data.id) {
      active[i] = data
      break
    }
  }
  return {
    active: active
  }
}