compatible

self

使用 self 而不是 window，获取全局作用域，可以让全局作用域的获取 不仅生效在浏览器，同时生效在 web worker 中
The Window.self read-only property returns the window itself, as a WindowProxy. It can be used with dot notation on a window object (that is, window.self) or standalone (self). The advantage of the standalone notation is that a similar notation exists for non-window contexts, such as in Web Workers. By using self, you can refer to the global scope in a way that will work not only in a window context (self will resolve to window.self) but also in a worker context (self will then resolve to WorkerGlobalScope.self).