¿Alguien puede ayudarme a entender por qué console.log(this.getPlayerDuration()) dentro de setAttendancePromptTimeLimit() devuelve NaN ?

 // video-player.js const videoP = document.querySelector('#in-course-player') class videoPlyer { constructor(videoElem){ this.vidPlayer = videoElem } play = function(cb){ arguments.length ? cb : console.log('play') } addListener = (elem, event, cb) => { elem.addEventListener(event, cb) } getPlayerCurrentTime = () => this.vidPlayer.currentTime getPlayerDuration = () => this.vidPlayer.duration showVideoDuration = function(cb){ arguments.length ? cb : this.addListener(this.vidPlayer, 'loadedmetadata', () => console.log(this.getPlayerDuration())) } setAttendancePromptTimeLimit = cb => { // returns NAN console.log(this.getPlayerDuration()) } init = () => { //returns 16.1 this.showVideoDuration() //returns NAN this.setAttendancePromptTimeLimit() } } const coursePlayer = new videoPlyer(videoP) coursePlayer.init()