Sry if its a silly question, I'm not soo good in JavaScript  Why can't I use:

for (let room of Game.rooms) {
  room.lookAt(1,1);
}

If i use "room IN Game.rooms" then I can't access the lookAt function again because I get the error:
"TypeError: room.lookAt is not a function"

Solution:
for (let room in Game.rooms) {
  Game.rooms[room].lookAt(1,1);
}

Thx Atavus for the answer!

var sources = creep.room.find(FIND_SOURCES);
var target = creep.room.find(FIND_MY_SPAWNS)[0];
var nearestSource = {source: sources[0], pathLength: 100000};
for(var i = 0; i < sources.length; i++) {
  var source = sources[i];
  var pathLength = creep.room.findPath(target.pos, source.pos).length;
  //var pathLength = PathFinder.search({pos: target.pos, range: 1}, {pos: source.pos, range: 1}).path;
  if (pathLength < nearestSource.pathLength)
    nearestSource = {source: source, pathLength: pathLength};
}

The outcommented code is the code that didn't work and produced the above error.
Thanks for your help!

TypeError: a.getRangeTo is not a function
at h:5:6733
at Object.c.search:5:11195
at Object.e.PathFinder.search:7:9249
at Object.helperMethods.findSource:39:41
at Object.roleHarvester.run:9:31
at Object.module.exports.loop:22:40
at __mainLoop:1:14194
at eval:2:4