get the length/duration (in milliseconds) of an audio file in JS, written in TS

getAudioClipDuration.ts

/**
 * returns a promise which when resolves returns the duration of the audio in milliseconds or 
 * rejects with the value if something goes wrong
 */
export function getDurationOfAudioInMilliseconds(src: string): Promise<number> {
    return new Promise((resolve, reject) => {
        var audio = new Audio();

        audio.addEventListener("loadedmetadata", function () {
            if (audio.duration) {
                resolve(audio.duration * 1000);
            } else {
                reject(audio.duration);
            }
        });
        audio.src = src;
    });
}