Async JavaScript examples

compare.js

function asyncWithCallbacks(callback){
  getApiUrl(apiName, function(err1, url){
    if(err1) throw new Error(err1);
    callApi(url, function(err2, data){
      if(err2) throw new Error(err2);
      writeDataToServer(data, function(err3, response){
        if(err3) throw new Error(err3);
        console.log('welcome to the third circle of callback hell.')
        callback(response);
      })
    })
  }
}

function asyncWithPromises(callback){
  getApiUrl(apiName)
    .then(url => callApi(url))
    .then(data => writeDataToServer(data))
    .then(response => {
      console.log('this is definitely better.')
      callback(response) // but this is still needed, I think
    })
    .catch(err => {
      console.log(err);
    })
}

async function asyncWithAwait(){
  try{
    const url = await getApiUrl(apiName);
    const data = await callApi(url);
    const response = await writeDataToServer(data);
    return response;
  } catch (err) {
    console.log(error);
  }
}

examples.js

const p1 = new Promise(function(resolve, reject){
	setTimeout(() => {
		resolve(1);
	}, 1000)
})

const p2 = new Promise(function(resolve, reject){
	setTimeout(() => {
		resolve(2);
	}, 2000)
})

const p3 = new Promise(function(resolve, reject){
	setTimeout(() => {
		resolve(3);
	}, 3000)
})

const f1 = async () => {
	return await p1
}

const f2 = async () => {
	return await p2
}

const f3 = async () => {
	return await p3
}

const waitForPromises = async () => {
	return await Promise.all([f1(), f2(), f3()])
}

const syncFunc = () => [8,9,10];

const controller = async () => {
	const s = new Date().getTime();
	const results = await waitForPromises()
	const syncResults = syncFunc();
	console.log(new Date().getTime() - s)
	console.log(results, syncResults)
	return syncResults;
}

module.exports = {
	waitForPromises,
	controller
}