flatten an array containing prev, next nested objects

flatten.js

function (obj, arr) {
  var index = arr.push(obj);
  if (obj.prev) {
    arr.splice.apply(arr, [index - arr.length, 0].concat(this.timeline(obj.prev, [])));
  }
  if (obj.next) {
    arr.splice.apply(arr, [index + arr.length, 0].concat(this.timeline(obj.next, [])));
  }
  return arr;
}