The read-only HTMLMediaElement property duration indicates the length of the element's media in seconds.
A double-precision floating-point value indicating the duration of the media in seconds. If no media data is available, the value NaN is returned. If the element's media doesn't have a known duration—such as for live media streams—the value of duration is Infinity.
const obj = document.createElement("video");
console.log(obj.duration); // NaNHTMLMediaElement.currentTime: The current playback position of the media<audio> and <video> elements