asyncAwaitExamples.ts

// This page demonstrates running multiple functions simultaneously
// and waiting on them to finish.

// Maybe you have an api call that takes 6 seconds...
// And you only need the response at the end

// Would you like to start a function and check if the promise is resolved later?
// Then check out the async/await and the promiseAll functions

main();

// Launches 3 types of functions
async function main() {
  await synchronousFunctions();
  await asyncAwait();
  await promiseDotAll();
}

// Synchronous (normal) Functions
async function synchronousFunctions() {
  const startTime = Date.now()
  console.log("----------- Synchronous (normal) Functions -----------")
  
  const message = await longFunction();
  await someOtherFunction();
  console.log("Awaited Message: ", message);

  console.log(`took: ${Date.now() - startTime} ms`);
}

// With promise and await
async function asyncAwait() {
  const startTime = Date.now()
  console.log("----------- With async / await -----------")

  const asyncPromise = longFunction();

  // Put consecutive code here
  // Code that can run while longFunction() is running
  someOtherFunction();
  // ...

  // Now wait for the first function
  const message = await asyncPromise;
  console.log("Awaited Message: ", message);

  console.log(`took: ${Date.now() - startTime} ms`);
}

// With Promise.all()
async function promiseDotAll() {
  const startTime = Date.now()
  console.log("----------- With Promise.all() -----------")

  Promise.all(
    [longFunction(), 
      someOtherFunction()])
  .then((response) => {
    console.log("Awaited Message: ", response[0]);
    console.log(`took: ${Date.now() - startTime} ms`);
  });
}

// ---- Helper FUnctions ----

// Function that may take a while
async function longFunction() {
  console.log("Started longFunction()");
  await sleep(6000);
  console.log("Finished longFunction()");
  return "Message Returned"
}

// Function you can do while waiting
async function someOtherFunction() {
  console.log("Started someOtherFunction()");
  await sleep(4000);
  //...
  console.log("Finished someOtherFunction()");
}

// Sleep this long
function sleep(ms){
  return new Promise(resolve=>{
      setTimeout(resolve,ms)
  })
}