Pause Inactive Tab Using visibilitychange

inactive.js

var forced = false;
var pauseWhileInactive = function() {
    switch (document.visibilityState) {
        case 'hidden' :
            if (!sfx.volume.value) return;
            forced = sfx.volume.value;
            sfx.volume.value = 0;
            break;
        case 'visible' :
            if (!forced) return;
            sfx.volume.value = forced;
            forced = false;
            break;
    }
};
document.addEventListener('visibilitychange', pauseWhileInactive);