change common video the option style.display not change none

[R8KwEwN2hvrhY]

Video.js 7.21.1
videojs-contrib-quality-levels @Version 3.0.0
videojs-http-source-selector v1.1.5

i in my scrpt add
if (player.qualityLevels().length==0) {
document.getElementsByClassName("vjs-http-source-selector vjs-menu-button vjs-menu-button-popup vjs-control vjs-button")[0].style.display = 'none';
}
else {
document.getElementsByClassName("vjs-http-source-selector vjs-menu-button vjs-menu-button-popup vjs-control vjs-button")[0].style.display = 'block';
};
it's setInterval,so not good,i want to know player.qualityLevels().length has something the best time,or some other way to change that