cmisFolders.coffee

folders = [
  {id:1, parentId:2, childrenId:[]}
  {id:2, parentId:null, childrenId:[]}
  {id:3, parentId:2, childrenId:[]}
  {id:4, parentId:5, childrenId:[]}
  {id:5, parentId:3, childrenId:[]}
  {id:6, parentId:5, childrenId:[]}
  {id:7, parentId:999, childrenId:[]}
  {id:8, parentId:7, childrenId:[]}
]

findParent = (childId, parentId) ->
  parent = (f for f in folders when f.id is parentId)?[0]
  return if not parent or parent.childrenId.indexOf(childId) > -1
  parent.childrenId.push childId
  findParent parent.id, parent.parentId

for folder in folders
  findParent folder.id, folder.parentId

console.log folders