Because it uses hidden classes to get read in O(1) for an object property access. The slowdown comes from the inline cache as explained in below article. https

Because it uses hidden classes to get read in O(1) for an object property access. The slowdown comes from the inline cache as explained in below article. https://richardartoul.github.io/jekyll/update/2015/04/26/hidden-classes.html https://richardartoul.github.io/jekyll/update/2015/04/26/hid...