What the browser can actually tell you about your hardware (and what it can't)

I spent a while building browser-based hardware diagnostics and came away with a much clearer sense of where the web platform is genuinely capable and where it quietly lies to you. Notes below, with live demos for each API so you can poke at them yourself. Refresh rate: requestAnimationFrame is the only signal you get There's no screen.refreshRate . The only approach is timing requestAnimationFrame callbacks and inferring the rate from the median frame delta: const deltas = []; let last = performance . now (); function tick ( now ) { deltas . push ( now - last ); last = now ; if ( deltas . length < 180 ) requestAnimationFrame ( tick ); else { const sorted = deltas . slice (). sort (( a , b ) => a - b ); console . log ( Math . round ( 1000 / sorted [ sorted . length >> 1 ])); } } requestAnimationFrame ( tick ); Two gotchas that cost me time. Use the median , not the mean — a single dropped frame wrecks an average. And browsers throttle rAF in background tabs, so the measurement is meaningless unless the tab is visible; gate it on document.visibilityState . ( live version ) Screen dimensions: four different answers, all "correct" screen.width , window.innerWidth , window.devicePixelRatio and screen.availWidth measure genuinely different things, and the one people usually want — actual native panel resolution — is screen.width * devicePixelRatio . Except that's still CSS-pixel derived, so on a scaled display it can disagree with what the panel physically is. The browser simply does not expose true hardware resolution. ( demo ) Keyboard: event.code vs event.key , and the keys you never receive event.key is layout-dependent, event.code is physical position — for a hardware tester you want code . The real limitation is that some keys never reach JS at all: PrintScreen often doesn't fire keydown , Meta combinations get swallowed by the OS, and Fn isn't a browser-visible key on most laptops. N-key rollover testing works surprisingly well though, since you just track the siz