showToast.js

function success() {
  run(showToast("pass"));
}

function* showToast(message) {
  var div = document.createElement("div");
  div.className = "toast in";
  div.textContent = message;
  document.body.appendChild(div);
  yield delay(1000);
  div.className = "toast out";
  yield delay(500);
  document.body.removeChild(div);
}

function run(g) {
  const { value, done } = g.next();
  if (!done) {
    value.then(() => run(g));
  }
}

function delay(ms) {
  return new Promise(r => setTimeout(r, ms));
}