浏览器和js引擎在window里添加了很多的全局属性（比如，js API如localStorage）， 所以找到所有的全局引用就像干草堆里找面条（大海捞针）
新建iframe ，指向blank， 获取window的属性也就是全局变量
This utility can easily run in a Continuous Integration context (e.g., in E2E tests using Cypress) to provide automated feedback.
I recommend running this utility in browser tabs with no extensions: most browser extensions inject global variables in the window object, adding noise to the result (e.g., __REACT_DEVTOOLS_BROWSER_THEME__, etc. from the React DevTools extension).