gistfile1.js

var MAX_DEPTH = 3;

var findPath = function (source, target, u2f, visitor) { // u2f = user to friend

  var dist = {}
  var prev = {}
  var queue = []

  dist[source] = 0
  prev[source] = source
  queue[queue.length] = source

  while (queue.length > 0) {
    var cur = queue.shift() // pop the front element
    var d = dist[cur]

    if (cur == target) {
      var path = []
      var pos = target
      while (prev[pos] != pos) {
        path.unshift(pos)
        pos = prev[pos]
      }
      visitor(source, target, path)
      return d
    }

    if (d > MAX_DEPTH)
       return d

    var friends = u2f[cur]
    for (var fi = friends.length; fi--; ) {
      var next = friends[fi]
      var nextd = next in dist ? dist[next] : 987654321 // inf 
      if (d + 1 < nextd) {
         dist[next] = d + 1
         prev[next] = cur
         queue[queue.length] = next
      }
    }
  }
  return dist[target]
}

findPath;