lessons-remaining.js

var remaining = 0;

for(var i = 0; i < lessons_left.length; ++i) {
    var current = lessons_left[i];
    var text = current.textContent; 
    var idx = text.indexOf("/");
    
    if (idx > 0) {
        remaining += parseInt(text.substr(idx + 1))
    }
    
}

console.log("You have N lessons remaining: " + remaining);