Grokkable Concurrent JavaScript - Teaching Asynchronous Patterns and Refactorings

callback-purgatory-0.js

const get = require('./get'); // get(url, callback)

const githubApi = 'https://api.github.com';
const githubEventsUrlFor = username => `${githubApi}/users/${username}/events`;
const githubRepoUrlFor = repo => `${githubApi}/repos/${repo}`;

const fetchReposForLatestActivity = (user, callback) => {
  let timeout = setTimeout(function() {
    callback(new Error('Timed out'));
  }, 3000);

  get(githubEventsUrlFor(user), (err, allEvents) => {
    if (err) {
      return callback(err);
    }

    const events = allEvents.slice(0, 3);
    const repos = [];
    let remainingCount = events.length;

    events.forEach(event => {
      get(githubRepoUrlFor(event.repo.name), (err, data) => {
        if (err) {
          return callback(err);
        }

        repos.push({
          author: data.owner.login,
          avatar: data.owner.avatar_url,
          name: data.name,
          full_name: data.full_name,
          url: data.html_url,
          description: data.description
        });

        remainingCount -= 1;

        if (remainingCount <= 0) {
          clearTimeout(timeout);
          callback(null, repos)
        }
      });
    });
  });
};

fetchReposForLatestActivity('machuga', (err, repos) => {
  if (err) {
    console.error(err);
    return;
  }

  console.log(repos);
});

callback-purgatory-1.js

const get = require('./get'); // get(url, callback)

const githubApi = 'https://api.github.com';
const githubEventsUrlFor = username => `${githubApi}/users/${username}/events`;
const githubRepoUrlFor = repo => `${githubApi}/repos/${repo}`;

const fetchRepo = (repoName, callback) => {
  get(githubRepoUrlFor(repoName), callback);
};

const fetchEventsForUser = (user, callback) => {
  get(githubEventsUrlFor(user), callback);
};

const fetchReposForEvents = (events, callback) => {
  const repos = [];
  let remainingCount = events.length;

  events.forEach(event => {
    fetchRepo(event.repo.name, (err, data) => {
      if (err) {
        return callback(err);
      }

      repos.push({
        author: data.owner.login,
        avatar: data.owner.avatar_url,
        name: data.name,
        full_name: data.full_name,
        url: data.html_url,
        description: data.description
      });

      remainingCount -= 1;

      if (remainingCount <= 0) {
        callback(null, repos)
      }
    });
  });
};

const fetchReposForLatestActivity = (user, callback) => {
  let timeout = setTimeout(function() {
    callback(new Error('Timed out'));
  }, 3000);

  fetchEventsForUser(user, (err, allEvents) => {
    if (err) {
      return callback(err);
    }

    fetchReposForEvents(allEvents.slice(0, 3), (err, repos) => {
      if (err) {
        return callback(err);
      }

      clearTimeout(timeout);
      callback(null, repos);
    });
  });
};

fetchReposForLatestActivity('sgrif', (err, repos) => {
  if (err) {
    console.error(err);
    return;
  }

  console.log(repos);
});

callback-purgatory-2-multiple-callbacks.js

const callbacks = [
	(done) => { setTimeout(() => { done(null, '1') }, 500) },
	(done) => { setTimeout(() => { done(null, '2') }, 200) },
];

const whenAllSettled = (fns, callback) => {
	const results = [];
	let remainingCount = fns.length;

  const done = (i) => (err, result) => {
		let resultObject;

		if (err) {
			resultObject = { type: 'failure', value: err };
		} else {
			resultObject = { type: 'success', value: result };
		}

		results[i] = resultObject;

		remainingCount -= 1;

		if (remainingCount <= 0) {
			callback(null, results);
		}
	};

	fns.forEach((fn, i) => {
		fn(done(i));
	});
}

whenAllSettled(callbacks, (err, results) => {
	console.log("All done with round 1!", results);

	whenAllSettled([
		(done) => { setTimeout(() => done(new Error('oops')), 500); }
	], (err, results) => {
		console.log("All done with round 2!", results);
	})
});

eventloop-basics.js

console.log("first");

setTimeout(function fifth() { console.log("fifth"); }, 500);
setTimeout(function third() { console.log("third"); }, 0);
setTimeout(function fourth() { console.log("fourth"); }, 0);

console.log("second");

eventloop-boss-fight.js

const startTime = Date.now();
console.log("first at", startTime)

announceTick();

setTimeout(createTickLoggerFor("seventh"), 500);
setTimeout(createTickLoggerFor("third"), 0);
setTimeout(function differentTick() {
  announceTick();

  logWithOffset("fourth");
  setTimeout(createTickLoggerFor("sixth"), 0);

  for (let i = 0; i < 100000; i++) {
    process.stdout.write(`Delaying: ${i}\r`);
  }

  console.log('\n');

  logWithOffset("fifth");

  setTimeout(createTickLoggerFor("eighth"), 300);
}, 0);

logWithOffset("second");

function timeFromStart() {
  return Date.now() - startTime;
}

function createTickLoggerFor(msg) {
  return function() {
    announceTick();
    logWithOffset(msg);
  }
}

function logWithOffset(msg) {
  console.log(`[Offset: ${timeFromStart()}]: ${msg}`);
}

function announceTick() {
  process.nextTick(() => {
    console.log("-----TICK-----")
  });
}

Gist will not update 2 file to use 2 spaces or tabs. I am so sorry, internet. I have failed you 😢