sample.js

/* App.makeProps */
static makeProps($) {
  return {
    /* call Box.makeProps to construct the substate */
    box1: [Box, "1"],
    box2: [Box, "2"],
    /* call OtherData.makeProps to get the substate */
    OtherData
  }
}

/* Box.makeProps */
static makeProps($, dispatch, id) {
  return {
    top: $["box" + id].top || 0,
    left: $["box" + id].left || 0,
  }
}