If you look at the bottom left of the screen, it is live compiling/rendering a 3D particle swarm animation while you edit the code, so really not so surprising that it makes the machine work a bit.

On my laptop (a Core i7 Chromebook - fast but not crazy by HN standards) the fan runs for a half second at first load - presumably during the compilation step - then shuts off immediately.

try using a better web browser ?