lookup.js

function lookup(obj /*Object */, props/* String */){
  if ( ! (obj && props)) { return undefined; }

  var ps = props.split('.');
  var pointer = obj;
  var val = undefined;
  var i = 0, len = ps.length;

  for(;i<len;i++) {
    pointer = pointer[ps[i]];
    if ('undefined' === typeof pointer) {
      break;
    }
  }

  if (i === len) { val = pointer; }

  return val;
}

lookup({a:{b:{c:'a'}}}, 'a.b.c'); // == a
lookup({a:{b:{c:'a'}}}, 'a.b.e'); // == undefined