simple async loader

var loaded = 1;

for(i=0; i<10; i++){
  var f = (function (n) {
    setTimeout(function () {
      console.log(n, loaded++); // do callback when loaded == 10;
    }, Math.random() * 3000)
  })(i) 
}

the way of the promise

let load = src => {
    return new Promise(function(resolve, reject) {
        let o = document.createElement('script');
	o.async = o.defer = true;
	o.src = src;
        o.addEventListener('load', () => resolve(src));  // will resolve on script loaded event
        let s = document.getElementsByTagName('script')[0];
	s.parentNode.insertBefore(o, s.nextSibling);
    });
  }

let done = () => console.log('all done');
let uhoh = err => console.log(err);

Promise
  .all(urls.map(src => load(src)))
  .then(done)
  .catch(uhoh);

Things to talk about ...

• understands loops
• closures
• self-executing anonymous functions
• async programming (eg, won't execute in order)
• promises