Async JS

Event Loop
callbacks

function doLongRunningThingAndGiveAnswerAfter(someFunctionToCallLater) {
  setTimeout(function () {
    someFunctionToCallLater(42);
  }, 2000);
}

function someOtherFunctionThatGetsTheAnswer(answer) {
  // this will log after 2 seconds...
  console.log(answer);
}

doLongRunningThingAndGiveAnswerAfter(someOtherFunctionThatGetsTheAnswer);

Promises
- async / await
API Requests, JSON, fetch, cors