Now you’ve added a variable declaration, which makes life more painful for keeping your polyfill small. The name of the game in these things is minimising size—though I will allow that a more verbose form can be useful for teaching.
Worrying about keeping polyfills micro-optimized seems somewhat silly, when a typical website is pulling in megabytes of other scripts and trackers. Not to mention when just the headers and cookies on every request can balloon up into the tens or hundreds of kilobytes.
