Get Duration of a WesBos's Course.

duration.js

var mins = 0; 
var sec = 0;
durations = Array.from(document.querySelectorAll('.duration'))
durations.forEach(e => {
    mins += parseInt(e.textContent.split(":")[0]);
    sec += parseInt(e.textContent.split(":")[1]);
})
sec += (mins * 60)
new Date(sec * 1000).toISOString().substr(11, 8);