不对，如果在浏览器是指向window, Node中是global。

function sayThis() {
  console.log(this);
}
sayThis.call(undefined); // Window {speechSynthesis: SpeechSynthesis, caches: CacheStorage, localStorage: Storage, sessionStorage: Storage, webkitStorageInfo: DeprecatedStorageInfo…}

注意：当第一个参数为null或undefined时，将是JS执行环境的全局变量。浏览器中是window，其它环境（如node）则是global。

The value of this provided for the call to fun. Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object and primitive values will be converted to objects.

摘自MDN，已经解释得很清楚了。和theWalker说的一致