nem035

httpGet(url, once(processValue));

function once(cb) {
  var hasExecuted = false;
  return function callbackWrapper() {
    if (!hasExecuted) {
      hasExecuted = true;
      cb.apply(this, arguments);
    }
  }

nem035

httpGet(url1, function(res) {
  // here we'll receive value1
});

httpGet(url2, function(res) {
  // here we'll receive value2
});

function processValues(value) {
  // we want to call this function first for value1,

nem035

// this doesn't work
try {
  httpGet(function callback() {
    // an error caused asynchronously
    // cannot be caught via a callback
    // mechanism
  }) 
} catch (err) {
  // this will only get called if httpGet
  // itself throws a synchronous error

nem035

// when performing an async operation that requires a callback
// we have to immediately provide that callback
// and would need to maintain or pass around a reference to 
// the callback in our codebase if we wanted to handle the
// response in a different place from where we started the async
// process.
httpGet(function callback() {
  // we have to provide this callback immediately
  // when starting this operation and cannot do
  // it at a later point.

nem035

var globalState; // callbacks have to talk through global state

httpGet(function callback1(value) {
  globalState.callback1 = value;
})

httpGet(function callback2(value) {
  globalState.callback2 = value;
})

nem035

[1,2,3].forEach(function callback(num) {
  // this code runs synchronously
})
// this line isn't reached until the 
// array above is fully iterated on

nem035

function * fibonacciGen() {
  let prev1 = 1;
  let prev2 = 1;
  while (true) {
    let next = prev1 + prev2;
    yield prev1;
    prev1 = prev2;
    prev2 = next;
  }
}

nem035

var fn = co.wrap(function* (val) {
  // we can yield a promise
  // which behaves like await-ing it
  return yield Promise.resolve(val);
});

fn(true).then(function (val) {

});

nem035

function computeMaxCallStackSize() {
  try {
    return 1 + computeMaxCallStackSize();
  } catch (e) {
    return 1;
  }
}

nem035

function recurseForever() {
 recurseForever();
}
recurseForever();

// outputs
// Uncaught RangeError: Maximum call stack size exceeded