// Proof of concept: "for ... of" can iterate over array
// elements while doing async work on each element,
// usinmg "await", even in node 8. We don't need to
// wait for node 10 and "async iterators" for that, 
// although those do cool things too.

// This will always print the products in this order,
// even though they take a variable amount of time to "sell".
// This shows they are being awaited in sequence, one
// at a time, which is what we want.
//
// (Yes, there are cases where you want stuff to happen
// in parallel. For that Promise.all is the way to go)

const products = [
  'cheese',
  'trees',
  'cats'
];

// Do some asynchronous work to sell a product

async function sell(product) {
  await wait();
  console.log('sold ' + product);
}

async function main() {
  for (const product of products) {
    await sell(product);
  }
}

main();

// This is just a simple promise-ification of setTimeout,
// which is callback-driven. We might use `Promise.delay`
// from bluebird or some lighter wrapper for this. But
// here timeouts are just an example and we'd probably
// be doing more interesting async work like talking to
// a database

function wait() {
  return new Promise(function(resolve, reject) {
    setTimeout(resolve, Math.random() * 1000);
  });
}