mightyguava

getUserData(function doStuff(e, a) {
  getMoreUserData(function doMoreStuff(e, b) {
    getEvenMoreUserData(function doEvenMoreStuff(e, c) {
      getYetMoreUserData(function doYetMoreStuff(e, c) {
        console.log('Welcome to callback hell!');
      });
    });
  });
})

mightyguava

// Suppose that we have a method fetchJson() that does GET requests and has an interface that looks
// like this, where callback is expected to take error as its first argument and the parsed response
// data as its second.
function fetchJson(url, callback) { ... }
fetchJson('/api/user/self', function(e, user) {
  fetchJson('/api/interests?userId=' + user.id, function(e, interests) {
    var recommendations = [];
    interests.forEach(function () {
      fetchJson('/api/recommendations?topic=' + interest, function(e, recommendation) {
        recommendations.push(recommendation);

mightyguava

fetchJson('/api/user/self')
    .then(function (user) {
        return fetchJson('/api/user/interests?userId=' + self.id);
    })
    .then(function (interests) {
        return Promise.all[interests.map(i => fetchJson('/api/recommendations?topic=' + i))];
    })
    .then(function (recommendations) {
        render(user, interests, recommendations);
    });

mightyguava

fetchJson('/api/user/self')
    .then(function (user) {
      return fetchJson('/api/user/interests?userId=' + self.id)
          .then(interests => {
            user: user,
            interests: interests
          });
    })
    .then(function (blob) {
      return Promise.all[blob.interests.map(i => fetchJson('/api/recommendations?topic=' + i))]

mightyguava

co(function* () {
  var user = yield fetchJson('/api/user/self');
  var interests = yield fetchJson('/api/user/interests?userId=' + self.id);
  var recommendations = yield Promise.all(
      interests.map(i => fetchJson('/api/recommendations?topic=' + i)));
  render(user, interests, recommendations);
});

mightyguava

function* counts(start) {
  yield start + 1;
  yield start + 2;
  yield start + 3;
  return start + 4;
}
const counter = counts(0);
console.log(counter.next()); // {value: 1, done: false}
console.log(counter.next()); // {value: 2, done: false}
console.log(counter.next()); // {value: 3, done: false}

mightyguava

function* printer() {
  console.log("We are starting!");
  console.log(yield);
  console.log(yield);
  console.log(yield);
  console.log("We are done!");
}
const counter = printer();
counter.next(1); // We are starting!
counter.next(2); // 2

mightyguava

function makeCounter() {
  var count = 1;
  return function () {
    return count++;
  }
}
var counter = makeCounter();
console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3

mightyguava

function printer(start) {
  let state = 0;
  let done = false;
  function go(input) {
    let result;
    switch (state) {
      case 0:
        console.log("We are starting!");
        state = 1;
        break;

mightyguava

function* adder(initialValue) {
  let sum = initialValue;
  while (true) {
    sum += yield sum;
  }
}