pick or put value to object property defined by chain

pick_put.js

var pick = function(obj, chain) {
  var src = chain.split('.');
  var res = obj;

  for (var i = 0, l = src.length; i < l; ++i) {
    if (!(src[i] in res)) {
      return void(0);
    }
    res = res[src[i]];
  }
  return res;
};

var put = function(obj, chain, value) {
  var src = chain.split('.');
  var res = obj;
  
  for (var i = 0, l = src.length; i < l; ++i) {
    if (!(src[i] in res)) {
      res[src[i]] = {};
    }
    if (i + 1 === l) {
      res[src[i]] = value;
    } else {
      res = res[src[i]];
    }
  }
};