tti-fps.js

(function() {
    if (window !== top) return;

    const bucketSize = 500, threshold = 30, stamps = []
    function measureFps() {
        const now = performance.now()
        if (stamps.length) {
            while (now - stamps[0] > bucketSize) {
                stamps.shift()
            }

            const fps = stamps.length * 1000 / bucketSize
            if (fps >= threshold) {
                console.warn(`fps was ${fps} from ${stamps[0]} to ${now} -- tti=${stamps[0]}`);
                return;
            }
        }

        stamps.push(now)
        window.requestAnimationFrame(measureFps);
    }
    window.requestAnimationFrame(measureFps);
})();