code: function extendObj (obj, key, source) {
    obj[key] = obj[key] || {};
    for(var args = arguments, i = 2; i < args.length; i++) {
      source = args[i];
      for (var k in source)
        if (own(source, k)) obj[key][k] = source[k];
    }
    return obj[key]
  }
docs: var obj={a:{b:{c:1}}}; console.log(objGetObj(obj)) console.log(objGetObj(obj, [])) console.log(objGetObj(obj, 'a')) console.log(objGetObj(obj, 'a.b')) console.log(objGetObj(obj, 'a.b.c.e')) extend obj from source, if it's no key in obj, create one