Edit in JSFiddle

const structure = {
  /* Milliseconds since Epoch */
  "timestamp": "number",
  "organisation": "string",
  "type": "ReaderArrived",
  "location": {
    "id": "string",
    "name": "string", 
  },
  "reader": {
    "id": "string",
    "name": "string", 
  }
};