RAF Performance Check (Updated)

raf.js

/**
     * RAF Performance Checking
     *
     * Will enable and disable a flag on the window object
     * When Javascript performance suffers, so that optional features
     * Can be Disabled or delayed
     */
    (function () {
        var lastTimestamp = + new Date();

        /**
         * Compares the execution of requestAnimationFrame to it's ideal, 60fps.
         * When Javascript is performant, the difference should approach 16ms.
         * When experiencing degraded Javascript performance, this value will begin to increase.
         * If it reaches 32, we toggle the flag `window.performant`, which other
         * functions can use to turn off the execution of optional features
         */
        function perfCheck () {
            var difference = + new Date() - lastTimestamp;
            lastTimestamp = + new Date();

            window.performant = difference < 32;

            requestAnimationFrame(perfCheck);
        }

        requestAnimationFrame(perfCheck);
    })();