It just blew my mind! I suppose I shouldn't be surprised at all, JS was written for manipulating the DOM but I was NOT expecting a cool terminal style with a typing/Matrix-style transition animation from some of the first webpages ever.
My brain even ascribed a CRT distortion effect to it, even though that's not actually happening.
edit: okay, no, I am an idiot. Those pages were made in 2013:
https://line-mode.cern.ch/